Printing system, print controller, printing apparatus, method of controlling printing operation, method of printing, ink cartridge, ink supplier, and recording medium

ABSTRACT

A technique of the present invention uses dark yellow (DY) ink, in addition to a plurality of conventionally used basic color inks including cyan (C) ink, magenta (M) ink, and yellow (Y) ink. The technique may cause a printer to create dots with the DY ink, in place of creation of dots with the Y, C, and M inks. This arrangement enhances the degree of freedom in specification of dot on-off conditions of the respective inks, and relieves the restriction of ink duty, thereby enabling a resulting printed image to have higher picture quality.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a technique of forming anadequate distribution of ink dots of respective colors on a printingmedium, so as to print an image expressed in a wide range of naturalcolors.

[0003] 2. Description of the Related Art

[0004] In a printing apparatus that ejects ink droplets of various colorinks from a print head and thereby expresses an image of natural colorson a printing medium, four color inks, that is, cyan (C), magenta (M),yellow (Y), and black (K), are basically used to create ink dots andprint an image. The printing apparatus regulates the hue and thelightness, which are indexes representing the color, so as to print animage expressed in a wide range of natural colors. The hue, that is, the‘color’ or ‘tint’, such as red or blue, is regulated by changing theratio of dots of the C, M, and Y inks ejected from the print head. Thelightness is, on the other hand, regulated by changing the density ofdots. Regulating the ratio and the density of dots created with therespective color inks on the printing medium enables a printed image tohave a wide range of natural colors.

[0005] Some recently developed printing apparatus use light cyan (LC)ink and light magenta (LM) ink, (additionally light yellow (LY) ink insome cases) in addition to the above four basic color inks, so as tosignificantly improve the picture quality in an area of high lightness.In the case where an image in the area of high lightness (that is, thehighlighted area) is printed with only four color inks, C, M, Y, and K,a sparse distribution the C and M dots undesirably makes these dotsconspicuous and thereby lowers the picture quality of the printed image.The phenomenon of making the dots conspicuous to worsen the picturequality is expressed by the term ‘poor granularity’. It is difficult toreproduce the image information with regard to a fine part with thesparsely distributed dots. This is also the reason of the poor picturequality of the resulting printed image with only the four color inks, C,M, Y, and K. The dots of the LC and LM inks (additionally LY ink in someoccasions) are, on the other hand, not so conspicuous as the dots of theC and M dots and thereby do not lower the picture quality of thehighlighted area. The LC and LM inks enable the dots to be formed at ahigher density than the C and M inks. This accordingly enablesreproduction of the image information with regard to the fine part andfurther improves the picture quality. Because of these reasons, theprinting apparatus using the six color inks including the LC and LY inks(or the seven color inks further including the LY ink) improves thepicture quality of the highlighted area.

[0006] The prior art printing apparatus including those using the lightinks, however, can not sufficiently improve the picture quality in anarea of low lightness (that is, the shadow area), because of the reasonsdiscussed below. Especially the printing apparatus using the light inkshave an insufficient improvement in picture quality in the shadow area,while significantly improving the picture quality in the highlightedarea.

[0007] This problem is explained with an example of a gradation patternfrom red to black with a gradual decrease in lightness. The color ‘red’is reproduced by mixture of magenta dots and yellow dots. The lightnessis lowered by addition of cyan dots or black dots. Formation of blackdots on red dots makes the black dots extremely conspicuous in an areasupposed to have a homogeneous color. This results in the poorgranularity. The dots of cyan, which is complementary to red, are alsorather conspicuous on the red dots, although the degree ofconspicuousness is lower than that of the black dots. Formation of cyandots on red dots thus also results in the rather poor granularity. As inthe case of the highlighted area, the use of the light cyan inkeffectively improves the granularity. From the viewpoint of theimprovement in granularity, the light cyan ink is most preferable overthe cyan ink and the black ink to form dots over the red dots. Additionof the cyan dots or the black dots on the red dots having a sufficientlylow lightness, however, does not make the cyan dots or the black dots soconspicuous but keeps the granularity at a fair level.

[0008] There is a restriction of total quantity of ink ejected per unitarea on the printing medium, and it is impossible to heighten thedensity of dot formation limitlessly. This restriction is referred to asthe restriction of ink duty. Ejection of ink over the allowed density ofdots causes blots or wrinkles on the printing medium. In order to avoidsuch problems, each printing medium has a preset maximum density of dots(restriction of ink duty). The total density of dots created with therespective inks should not exceed this restriction of ink duty.

[0009] When the gradation pattern from red to black is printed, it isrequired to add the light cyan dots or the cyan dots. The color ‘red’ isoriginally expressed by a large number of yellow dots and magenta dotsas mentioned previously. Formation of even a small number of light cyandots or cyan dots thus causes the total quantity of ink to reach therestriction of ink duty. In the course of the gradation, there isaccordingly a prohibition of further addition of the light cyan dots orthe cyan dots. In the practical operation, when there is some margin forthe restriction of ink duty, light cyan dots are added to red dots tolower the lightness. When the total quantity of ink reaches therestriction of ink duty, even if the cyan dots may have adverse effectson the granularity of the resulting printed image, the cyan dots insteadof the light cyan dots should be formed to further decrease thelightness. When the total quantity of ink again reaches the restrictionof ink duty under the condition of the perfect replacement of the lightcyan dots with the cyan dots, even if the black dots are conspicuous,the black dots instead of the cyan dots should be formed to furtherdecrease the lightness. In the shadow area (the area of low lightness)having the gradation from red to black, the cyan dots and the black dotsare often used irrespective of their conspicuousness, because of therestriction of ink duty. This naturally results in the poor granularity.

[0010] The above description regards the example of printing thegradation pattern from red to black. The formation pattern of ink dotsshould be specified under the various limitations including theimprovement in granularity and the restriction of ink duty. The designof the optimum dot formation pattern accordingly requires a lot of timeand labor with the trial and error.

SUMMARY OF THE INVENTION

[0011] The object of the present invention is thus to enhance the degreeof freedom in specification of dot on-off conditions with regard to aplurality of different inks and thereby improve the picture quality in aspecific area including a low lightness area (shadow area).

[0012] At least part of the above and the other related objects isactualized by a printing system, which includes a printer that createsdots with a plurality of different inks, so as to print an image on aprinting medium, and a print controller that supplies controlinformation to the printer, so as to control the creation of dots withthe plurality of different inks. The print controller includes: a doton-off condition specification unit that specifies dot on-off conditionswith regard to a plurality of basic color inks and a dark ink based oninput image data, the plurality of basic color inks being combined withone another to express achromatic color, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; and acontrol information output unit that outputs the specification of thedot on-off conditions with regard to the plurality of basic color inksand the dark ink to the printer as the control information. The printerincludes: a control information input unit that receives thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink, which is output from the controlinformation output unit, as the control information; and a dot formationunit that creates dots with the plurality of basic color inks and thedark ink, based on the input control information.

[0013] The present invention is also directed to a method of printing,which corresponds to the printing system discussed above. The presentinvention accordingly provides a method of creating dots with aplurality of different inks, so as to print an image on a printingmedium. The method includes the steps of: specifying dot on-offconditions with regard to a plurality of basic color inks and a dark inkbased on input image data, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and creating dots with the plurality of basic colorinks and the dark ink, based on the specification of the dot on-offconditions with regard to the plurality of basic color inks and the darkink, so as to print an image.

[0014] In the printing system and the corresponding method of thepresent invention, the dot on-off conditions with regard to theplurality of basic color inks and the dark ink are specified, based onthe input image data. Here the plurality of basic color inks arecombined with one another to create ink dots and thereby expressachromatic color. The dark ink includes one basic color ink selected outof the plurality of basic color inks as a primary component and anotherink having a specific hue different from the hue of the selected basiccolor ink. The dark ink has a lower lightness than that of the selectedbasic color ink. The dark ink may alternatively have a different inkcomposition from that of the selected basic color ink but equivalentspectroscopic characteristics to those of the selected basic color ink.When the selected basic color ink is yellow ink, for example, the darkink may be obtained by adding adequate quantities of cyan and magentadyes to the yellow ink or by adding an adequate quantity of black dye tothe yellow ink. The technique of the present invention creates dots withthe plurality of basic color inks and the dark ink on the printingmedium, based on the specification of dot on-off conditions with regardto the respective inks, so as to print an image. This arrangementenables dots to be created with the dark ink having the characteristicsdiscussed above, as well as with the plurality of basic color inks. Thisenhances the degree of freedom in specification of dot on-off conditionsand thereby improves the picture quality of a resulting printed image.Specifying the dot on-off conditions with regard to not only the basiccolor inks but the dark ink results in improving the picture quality,because of the functions discussed below.

[0015] As mentioned above, the dark ink includes one basic color inkselected out of the plurality of basic color inks as a primary componentand another ink having a specific hue different from the hue of theselected basic color ink, and has a lower lightness than that of theselected basic color ink. A certain color conventionally expressed by acombination of the plurality of basic color inks may be expressible byonly the dark ink or by a combination of the dark ink with smallquantities of one or plural basic color inks. In such cases, expressionof the certain color by the combination of the dark ink with one orplural basic color inks requires a less total quantity of inks, comparedwith the expression of the certain color by the combination of theplurality of basic color inks. The use of the dark ink thus improves thepicture quality, which is worsened by the restriction of ink duty. Forexample, the use of the dark ink desirably keeps the fair granularity ina shadow area, where the granularity is readily worsened by therestriction of ink duty.

[0016] A print controller of the present invention is applicable to sucha printing system. The present invention is accordingly directed to aprint controller that supplies control information to a printer, whichcreates dots with a plurality of different inks, in order to control thecreation of dots with the plurality of different inks. The printercreates dots with a plurality of basic color inks as well as with a darkink, wherein the plurality of basic color inks are combined with oneanother to express achromatic color, and the dark ink has a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink. Theprint controller includes: a dot on-off condition specification unitthat specifies dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on input image data; and acontrol information output unit that outputs the specification of thedot on-off conditions with regard to the plurality of basic color inksand the dark ink to the printer as the control information.

[0017] The present invention is further directed to a method ofcontrolling a printing operation, which corresponds to the printcontroller discussed above. The present invention accordingly provides amethod of supplying control information to a printer, which creates dotswith a plurality of different inks on a printing medium, in order tocontrol the creation of dots with the plurality of different inks andthereby controlling a printing operation of the printer. The methodincludes the steps of: (a) specifying dot on-off conditions with regardto a plurality of basic color inks and a dark ink based on input imagedata, the plurality of basic color inks being combined with one anotherto express achromatic color, the dark ink having a main wavelengthregion of light absorption substantially identical with that of onebasic color ink selected out of the plurality of basic color inks but alower lightness than that of the selected basic color ink; and (b)outputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to the printer as thecontrol information, so as to control the printing operation of theprinter.

[0018] In the print controller and the corresponding method ofcontrolling the printing operation, the dot on-off conditions withregard to the plurality of basic color inks and the dark ink arespecified, based on the input image data. The specification of the doton-off conditions is supplied to the printer as the control informationto control creation of dots with the plurality of basic color inks andthe dark ink.

[0019] The technique of the present invention provides the plurality ofbasic color inks and the dark ink in the printer, which creates dotswith a plurality of different inks on a printing medium, and suppliesthe control information to the printer. This arrangement enablescreation of ink dots with the plurality of different inks including thedark ink, thus printing an image of high picture quality.

[0020] In accordance with one preferable application of the printcontroller and the corresponding method of controlling the printingoperation, a color conversion table is provided to store mappings oftints used to express a color image to combinations of the plurality ofbasic color inks and the dark ink to represent the tints. In thisapplication, the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink are specified by referring to thecolor conversion table.

[0021] The method of referring to the color conversion table enables thedot on-off conditions of the respective inks to be specified quickly andaccurately.

[0022] In accordance with another preferable application of the printcontroller, the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink are specified, based on a presetproportion regarding dots of the plurality of basic color inks and dotsof the dark ink.

[0023] When the dot on-off conditions are specified with regard to thedark ink as well as the plurality of basic color inks, the proportion ofthe dots with the respective inks may take a variety of values. Thearrangement of specifying the dot on-off conditions based on theproportion set equal to an appropriate value enables an image of highpicture quality to be printed.

[0024] In accordance with still another preferable application of theprint controller, the dark ink has lower lightness and saturation thanthose of one basic color ink selected out of the plurality of basiccolor inks. The dark ink is obtained, for example, by adding the dye ofanother ink to the selected basic color ink.

[0025] The use of the dark ink enhances the degree of freedom inspecification of the dot on-off conditions and thereby improves thepicture quality of the resulting printed image. The use of the dark ink,which is obtained by adding at least one dye of another ink to lower thelightness and the saturation, may enable a specific color conventionallyexpressed by a combination of the plurality of basic color inks to beexpressed by only the dark ink or by a combination of the dark ink withsmall quantities of one or plural basic color inks. The expression ofthe specific color by the combination of the dark ink with the basiccolor inks reduces the total quantity of inks and thus improves thepicture quality, which is worsened by the restriction of ink duty.

[0026] The dark ink may alternatively have a main wavelength region formost strongly absorbing a ray in a visible range, which is substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks, and a greater integral of light absorptivity in awavelength region, of the visible range than that of the selected basiccolor ink.

[0027] The use of the dark ink enhances the degree of freedom inspecification of the dot on-off conditions and thereby improves thepicture quality of the resulting printed image.

[0028] The main wavelength region for most strongly absorbing a ray in avisible range is approximately equal to a range of 600 nm to 700 nm toabsorb a red ray in the case of cyan ink, equal to a range of 500 nm to600 nm to absorb a green ray in the case of magenta ink, and equal to arange of 400 nm to 500 nm to absorb a blue ray in the case of yellowink. Since the absorptivity of light gently varies, the half-width (thatis, the wavelength region having the absorptivity that is half themaximum absorptivity) may be adopted in the case where there is adifficulty in identifying the wavelength region.

[0029] The dark ink may have the main wavelength region, which is mostlyincluded in a wavelength region of 400 nm to 500 nm, and a smaller lightabsorptivity in the vicinity of 700 nm than a mean light absorptivity ina wavelength region of 600 nm to 700 nm.

[0030] It is known that the sensitivity of the vision of human eye tothe color gradually lowers in a wavelength range of about 650 nm and issignificantly low in the vicinity of 700 nm. Irrespective of a largevariation in spectroscopic characteristics of the ink in the vicinity ofthe wavelength of 700 nm, there is no significantly difference in huerecognized by the vision of the human eye. Namely the spectroscopiccharacteristics of the ink have a large degree of freedom in thevicinity of the wavelength of 700 nm. The ink having a favorable hue isthus prepared by utilizing this large degree of freedom. The dark inkhaving the favorable hue has the smaller light absorptivity in thevicinity of 700 nm than the mean light absorptivity in the wavelengthregion of 600 nm to 700 nm. The main wavelength region that is mostlyincluded in the wavelength region of 400 nm to 500 nm is substantiallyopposite to the range in the vicinity of 700 nm having the large degreeof freedom across the visible range. This facilitate the design of theink.

[0031] The dark ink may have the main wavelength region, which is mostlyincluded in a wavelength region of 400 nm to 500 nm, and a greater lightabsorptivity in the vicinity of 700 nm than a mean light absorptivity ina wavelength region of 600 nm to 700 nm. The greater light absorptivityin the vicinity of 700 nm than the mean light absorptivity in thewavelength region of 600 nm to 700 nm enables the dark ink to have amore preferable hue, because of the reason discussed above.

[0032] The dark ink, whose dot on-off conditions are specified by theprint controller of the present invention may have:

[0033] (A) a characteristic wavelength region for strongly absorbing aray in a visible range to mainly determine the hue of the dark ink,which is substantially identical with a characteristic wavelength regionof one basic color ink selected out of the plurality of basic colorinks;

[0034] (B) a mean value of light absorptivity that is greater than orsubstantially identical with a mean value of light absorptivity of theselected basic color ink in the characteristic wavelength region of thedark ink; and

[0035] (C) a mean value of light absorptivity that is greater than amean value of light absorptivity of the selected basic color ink in awavelength region of visible light except the characteristic wavelengthregion of the dark ink.

[0036] The dark ink satisfying the above condition (A) has a hue closeto the hue of the corresponding basic color ink, so that a specificcolor conventionally expressed by a combination of the plurality ofbasic color inks is, in many cases, expressible by a combination of thedark ink with one or plural basic color inks. Expression of the specificcolor by the combination of the dark ink satisfying the above conditions(B) and (C) with one or plural basic color inks requires the less totalquantity of inks than expression of the specific color by thecombination of the plurality of basic color inks. The use of the darkink satisfying all the above conditions (A) through (C) thus reduces thetotal quantity of ink consumption in many cases. This arrangementeffectively prevents the poor granularity and improves the picturequality, which is worsened by the restriction of ink duty as discussedpreviously.

[0037] The dark ink may have the characteristic wavelength region, whichis mostly included in a wavelength region of 400 nm to 500 nm, and asmaller light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.

[0038] As described above, even when the light absorptivity in thevicinity of 700 nm varies, the hue of the ink recognizable by the visionof the human eye does not have any significant variation. It isaccordingly expected that the spectroscopic characteristics of the inkhave a large degree of freedom in the vicinity of the wavelength of 700nm. The smaller light absorptivity in the vicinity of 700 nm than themean light absorptivity in the wavelength region of 600 nm to 700 nmenables the dark ink to have a more favorable hue. Setting thecharacteristic wavelength region of the dark ink to be substantiallyopposite to the range in the vicinity of 700 nm having the large degreeof freedom across the visible range facilitates the design of the ink.

[0039] The dark ink may have the characteristic wavelength region, whichis mostly included in a wavelength region of 400 nm to 500 nm, and agreater light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.

[0040] As described previously, there is a large degree of freedom insetting the light absorptivity in the vicinity of the wavelength of 700nm. The greater light absorptivity in the vicinity of 700 nm than themean light absorptivity in the wavelength region of 600 nm to 700 nm mayenable the dark ink to have a more favorable hue.

[0041] The dark ink, whose dot on-off conditions are specified by theprint controller of the present invention, may have a hue in a specifichue range interposed between a red hue zone and a green hue zone on aMunsell hue circle, and have a lower lightness than that of a basiccolor ink out of the plurality of basic color inks, which has a hue inthe specific hue range.

[0042] The specific hue range interposed between the red hue zone andthe green hue zone on the Munsell hue circle roughly corresponds to thehue of yellow. The color of yellow has a relatively high lightness. Dotsof the dark yellow ink having the lower lightness than that of theyellow ink are still not conspicuous. Creating dots with such a dark inkthus significantly improves the picture quality of the resulting printedimage.

[0043] The dark ink may have a hue in the specific hue range thatincludes a yellow hue zone and extends to a boundary between the yellowhue zone and the green hue zone on the Munsell hue circle. The ink inthis specific hue range has the hue of greenish yellow. Creating dotswith such a dark ink significantly improves the picture quality of theresulting printed image having the little greenish hue.

[0044] The dark ink may have a hue in the specific hue range thatincludes a yellow hue zone and extends to a boundary between the yellowhue zone and the red hue zone on the Munsell hue circle, and a smallersaturation than that of flesh color. The ink in the specific hue rangethat includes the yellow hue zone and extends to the boundary betweenthe yellow hue zone and the red hue zone on the Munsell hue circle hasthe hue of reddish yellow. Creating dots with such a dark inksignificantly improves the picture quality of the resulting printedimage having the little reddish hue. The color that is included in thespecific hue range and has a relatively large saturation is close to the‘flesh color’. When the ink having the hue of reddish yellow is used asthe dark ink, it is preferable that the ink has a smaller saturationthan that of flesh color. The dark ink of smaller saturationsignificantly improves the picture quality of the resulting printedimage. It is accordingly preferable that the dark ink has a hue in thespecific hue range that includes the yellow hue zone and extends to theboundary between the yellow hue zone and the red hue zone on the Munsellhue circle, and a smaller saturation than that of flesh color.

[0045] The dark ink may have a hue included in a specific range of 10Rto 10GY on a Munsell hue circle, and a lower lightness than that of abasic color ink out of the plurality of basic color inks, which has ahue in the specific range.

[0046] The ink in the specific range roughly has the hue of yellow.Creating dots with such a dark ink significantly improves the picturequality of the resulting printed image.

[0047] The dark ink may have a saturation of smaller than 3.5C on aMunsell chroma when the hue of the dark ink is in a range of 2.5YR to7.5YR on the Munsell hue circle.

[0048] The ink having the hue in the range of 2.5YR to 7.5YR on theMunsell hue circle and the saturation of greater than 3.5C on theMunsell chroma has the tint close to the flesh color. When an imagehaving the greenish hue is printed, the use of the dark ink having asmaller saturation than that of ‘flesh color’ has better effects onimprovement of the picture quality. It is accordingly preferable thatthe dark ink has a saturation of smaller than 3.5C on the Munsell chromawhen the hue of the dark ink is in the range of 2.5YR to 7.5YR on theMunsell hue circle.

[0049] The hue of the dark ink may be in a range of 10YR to 10GY on theMunsell hue circle. The ink in this range has the hue of greenishyellow. Creating dots with such a dark ink significantly improves thepicture quality of the resulting printed image having the littlegreenish hue.

[0050] The dark ink may have the hue in a range of 10Y to 10R on theMunsell hue circle and a saturation of smaller than 3.5C on a Munsellchroma. The ink having the hue in the range of 10Y to 10R on the Munsellhue circle and the saturation of greater than 3.5C on the Munsell chromahas the tint close to the flesh color. When an image having the reddishhue is printed, the use of the dark ink having a smaller saturation thanthat of ‘flesh color’ has better effects on improvement of the picturequality. It is accordingly preferable that the dark ink has the hue in arange of 10Y to 10R on the Munsell hue circle and a saturation ofsmaller than 3.5C on the Munsell chroma.

[0051] In accordance with one preferable application of the printcontroller that specifies the dot on-off conditions of the respectiveinks based on the image data, the technique specifies the dot on-offconditions with regard to the plurality of basic color inks and the darkink, as well as with regard to at least one light ink, which has a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink. The results of thespecification are output to the printer as the control information tocontrol the creation of dots with the plurality of different inks. Theprinter creates dots with the plurality of basic color inks, the darkink, and the at least one light ink on a printing medium, according tothe control information.

[0052] As described previously, the printing apparatus using the lightink remarkably improves the picture quality in the highlighted area buthas less effects on improvement of the picture quality in the shadowarea, because of the restriction of ink duty. Additionally using thedark ink improves the picture quality in the shadow area and thusattains the improvement in picture quality in the whole image.

[0053] In accordance with one preferable application of the printcontroller that specifies the dot on-off conditions of the respectiveinks based on the image data, the technique outputs the controlinformation to control the creation of dots to a printer that creates atleast two variable-size dots having different sizes with the respectiveinks. The technique specifies the dot on-off conditions as well as thesizes of the dots to be formed by the printer with regard to theplurality of different inks and supplies the results of thespecification to the printer. The printer creates the adequate size dotswith the plurality of different inks, based on the control information.

[0054] Varying the size of the ink dot by the printer that enablescreation of at least two variable-size dots having different sizessignificantly improves the picture quality of the resulting printedimage. In this application, using the dark ink enhances the degree offreedom in specification of the dot on-off conditions and improves thepicture quality, which is worsened by the restriction of ink duty.

[0055] In accordance with one preferable application of the printcontroller that specifies the dot on-off conditions of the respectiveinks based on the image data and the corresponding method of controllingthe printing operation, the technique specifies the dot on-offconditions with regard to the plurality of basic color inks, whichinclude at least yellow ink, as well as with the dark yellow ink, whichhas a main wavelength region of light absorption substantially identicalwith that of the yellow ink but a lower lightness than that of theyellow ink. The results of the specification are output to a printerthat enables creation of dots with the plurality of basic color inks andthe dark yellow ink. The printer receives the specification of the doton-off conditions and creates dots with the plurality of basic colorinks including at least the yellow ink and with the dark yellow ink, soas to print an image.

[0056] The yellow ink has a relatively high lightness. Even the darkyellow ink, which is darker than the yellow ink, still has a highlightness, so that dots of the dark yellow ink are relativelyinconspicuous. Creation of dots with the dark yellow ink thussignificantly improves the picture quality of the resulting printedimage.

[0057] In accordance with one preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to at least the cyan ink, the magenta ink, and theyellow ink as the plurality of basic color inks. In this case, the darkink may have a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink. Specification of thedot on-off conditions with regard to the dark ink is carried out toenable dots with the dark ink to be created together with dots of atleast one of the basic color inks when an image to be printed has huesvarying from red to green on a Munsell hue circle.

[0058] The image having hues varying from red to green on the Munsellhue circle is printed by adequately creating dots of the magenta ink ordots of the cyan ink together with the dots of the yellow ink. Thetechnique of this application enables the image having such hues to bealternatively printed by adequately creating dots of the dark inktogether with the dots of the basic color ink. This arrangementeffectively enhances the degree of freedom in specification of the doton-off conditions with regard to each color ink, thereby improving thepicture quality of the resulting printed image.

[0059] In accordance with one preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to at least the cyan ink, the magenta ink, and theyellow ink as the plurality of basic color inks. In this case, the darkink may have a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink. Specification of thedot on-off conditions with regard to the dark ink is carried out toenable dots with the dark ink to be created prior to creation of dotswith either one of the cyan ink and the magenta ink when an image to beprinted has hues varying from yellow to black.

[0060] Dots of the magenta ink or the cyan ink are rather conspicuous inan yellow image, unless the yellow image has a sufficiently lowlightness. When an image to be printed has hues varying from yellow toblack, creation of dots with the dark ink prior to creation of dots withthe magenta ink or the cyan ink lowers the lightness of the image andmakes the dots of the magenta ink or the cyan ink sufficientlyinconspicuous. The hue of the dark ink is closest to the hue of theyellow ink. Creation of dots with the dark ink in the yellow image priorto creation of dots with the magenta ink or the cyan ink accordinglydoes not make the dots of the dark ink conspicuous to lower the picturequality. Using the dark ink having the above characteristics thuspreferably improves the picture quality of the resulting printed image.The dots of the light cyan ink, which has the lower density than that ofthe cyan ink, and the dots of the light magenta ink, which has the lowerdensity than that of the magenta ink, are not so conspicuous in an imagehaving a relatively high lightness. Dots of the dark ink may thus becreated in an overlapping manner on the dots of the light cyan ink or onthe dots of the light magenta ink. In the case of a variable-dotprinter, small-size dots are not so conspicuous even when they arecreated in an image having a relatively high lightness. Like in the caseof the light ink, dots of the dark ink may thus be created in anoverlapping manner on the small-size dots of the cyan ink or on thesmall-size dots of the magenta ink.

[0061] In accordance with one preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to at least the cyan ink, the magenta ink, and theyellow ink as the plurality of basic color inks. In this case, the darkink may have a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink, and a lower lightnessthan that of the yellow ink. Specification of the dot on-off conditionswith regard to the dark ink is carried out to enable dots with the darkink to be created prior to creation of dots with either one of the cyanink and the magenta ink when an image to be printed has hues varyingfrom color of the either one of the cyan ink and the magenta ink toblack.

[0062] Dots of the cyan ink in a magenta image or dots of the magentaink in a cyan image are rather conspicuous, unless the image has asufficiently low lightness. When an image to be printed has hues varyingfrom magenta to black or hues varying from cyan to black, creation ofdots with the dark ink prior to creation of dots with the magenta ink orthe cyan ink desirably lowers the lightness of the image and makes thedots of the magenta ink or the cyan ink sufficiently inconspicuous. Thedark ink has the hue closest to the hue of the yellow ink. Like the dotsof the yellow ink, dots of the dark ink are thus relativelyinconspicuous in both the magenta image and the cyan image. Creation ofdots with the dark ink prior to creation of dots with the magenta ink orthe cyan ink accordingly does not make the dots of the dark inkconspicuous to lower the picture quality. Using the dark ink having theabove characteristics thus preferably improves the picture quality ofthe resulting printed image. The dots of the light cyan ink and the dotsof the light magenta ink are not so conspicuous in an image having arelatively high lightness. Dots of the dark ink may thus be created inan overlapping manner on the dots of the light cyan ink or on the dotsof the light magenta ink. In the case of a variable-dot printer,small-size dots are not so conspicuous even when they are created in animage having a relatively high lightness. Like in the case of the lightink, dots of the dark ink may thus be created in an overlapping manneron the small-size dots of the cyan ink or on the small-size dots of themagenta ink.

[0063] In accordance with one preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to at least the cyan ink, the magenta ink, and theyellow ink as the plurality of basic color inks. In this case, the darkink may have a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink, and a lower lightnessthan that of the yellow ink. Specification of the dot on-off conditionswith regard to the dark ink is carried out to enable dots with the darkink to be created after creation of dots with the yellow ink when animage to be printed has hues varying from color of either one of thecyan ink and the magenta ink to black.

[0064] Dots of the cyan ink in a magenta image or dots of the magentaink in a cyan image are rather conspicuous, unless the image has asufficiently low lightness. Creating yellow dots in such images lowersthe lightness of the image to some extent. The dots of the cyan ink orthe magenta ink may, however, be still rather conspicuous in theseimages. This technique creates dots with the dark ink subsequent tocreation of dots with the yellow ink. This further lowers the lightnessof the image and makes the dots of the magenta ink or the cyan inksufficiently inconspicuous. The dark ink has the hue closest to the hueof the yellow ink. Like the dots of th yellow ink, dots of the dark inkare thus relatively inconspicuous in both the magenta image and the cyanimage. Using the dark ink having the above characteristics thuspreferably improves the picture quality of the resulting printed image.

[0065] In accordance with another preferable application of the printcontroller of the present invention, the dot on-off conditions arespecified with regard to the plurality of basic color inks including atleast the cyan ink, the magenta ink, and the yellow ink, as well as withregard to the light ink, which has a hue substantially identical withthe hue of the cyan ink or the magenta ink but a lower density than thatof the cyan ink or the magenta ink. In this case, the dark ink may havea hue that is closest to the hue of the yellow ink among the cyan ink,the magenta ink, and the yellow ink. Specification of the dot on-offconditions with regard to the dark ink is carried out to enable dotswith the dark ink to be created after creation of dots with the lightink when an image to be printed has hues varying from yellow to black.

[0066] Dots of the magenta ink or the cyan ink are rather conspicuous inan yellow image, unless the yellow image has a sufficiently lowlightness. When an image to be printed has hues varying from yellow toblack, formation of dots with the light ink desirably lowers thelightness of the image. Formation of dots with the dark ink in additionto with the light ink further lowers the lightness of the image andthereby makes the dots of the magenta ink and the cyan ink moreinconspicuous. The hue of the dark ink is closest to the hue of theyellow ink. The dots of the dark ink are thus inconspicuous in theyellow image and do not lower the picture quality. Using the dark inkhaving the above characteristics thus preferably improves the picturequality of the resulting printed image.

[0067] The light ink, whose dot on-off conditions are specified by theprint controller, may be light cyan ink having a hue substantiallyidentical with that of the cyan ink but a lower density than that of thecyan ink or light magenta ink having a hue substantially identical withthat of the magenta ink but a lower density than that of the magentaink. Dots of the dark ink may be created after creation of dots withthese light inks. More specifically dots of the dark ink may be createdafter creation of dots with both the light cyan ink and the lightmagenta ink.

[0068] Creating dots with these light inks lowers the lightness in anyellow image. Creating dots with the dark ink further lowers thelightness in the yellow image. This makes the dots of the cyan ink andthe magenta ink more inconspicuous and improves the picture quality ofthe resulting printed image.

[0069] In accordance with one preferable application of the printcontroller that specifies the dot on-off conditions of the respectiveinks based on the image data and the corresponding method of controllingthe printing operation, the technique specifies dot on-off conditionswith regard to a plurality of basic color inks, which include at leastcyan ink, magenta ink, and yellow ink, as well as with dark yellow ink,which has a main wavelength region of light absorption substantiallyidentical with that of the yellow ink but a lower lightness than that ofthe yellow ink. The results of the specification are output to a printerthat enables creation of dots with the plurality of basic color inks andthe dark yellow ink. The printer receives the specification of the doton-off conditions and creates dots with the plurality of basic colorinks including at least the cyan ink, the magenta ink, and the yellowink and with the dark yellow ink, so as to print an image.

[0070] The yellow ink has a relatively high lightness. Even the darkyellow ink, which is darker than the yellow ink, still has a higherlightness than those of the cyan ink and the magenta ink. Dots of thedark yellow ink are accordingly not so conspicuous as dots of the cyanink or the magenta ink. Using the dark yellow ink in addition to thecyan ink, magenta ink, and the yellow ink to create dots and print animage thus significantly improves the picture quality of the resultingprinted image.

[0071] The printing apparatus of the present invention applicable to theprinting system discussed above may have another arrangement. Thepresent invention is accordingly directed to a printing apparatus thathas a print head to create dots with a plurality of different inks on aprinting medium, receives control information to control the creation ofdots with the plurality of different inks, and actually creates dotswith the plurality of different inks, based on the input controlinformation, so as to print an image. The printing apparatus includes: abasic color ink supply unit that supplies a plurality of basic colorinks to the print head, the plurality of basic color inks being combinedwith one another to express achromatic color; a dark ink supply unitthat supplies a dark ink to the print head, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; acontrol information input unit that receives the control informationwith regard to dots of the plurality of basic color inks and the darkink; and a dot formation unit that drives the print head based on theinput control information, so as to create dots with the plurality ofbasic color inks and the dark ink.

[0072] The present invention is also directed to a method of printing,which corresponds to the printing apparatus of the above configuration.The present invention thus provides a method of receiving controlinformation to control creation of dots with a plurality of differentinks and driving a print head, which creates dots with the plurality ofdifferent inks on a printing medium, based on the control information,so as to print an image. The method includes the steps of: (a) supplyinga plurality of basic color inks and a dark ink to the print head, theplurality of basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; (b) receiving the controlinformation with regard to dots of the plurality of basic color inks andthe dark ink; and (c) driving the print head based on the input controlinformation to create dots with the plurality of basic color inks andthe dark ink, thereby printing an image.

[0073] In the printing apparatus of the present invention and thecorresponding method of printing, the print head is driven according tothe input control information for controlling creation of dots withregard to the plurality of basic color inks and the dark ink. Dots withthe plurality of basic color inks and the dark ink are then created onthe printing medium to print an image.

[0074] The use of the dark ink in addition to the plurality of basiccolor inks enhances the degree of freedom in specification of dot on-offconditions and thus enables the adequate specification of the dot on-offconditions. The supplies of the plurality of basic color inks and thedark ink are fed to the print head, and the print head is then drivenaccording to the results of the specification of the dot on-offconditions. This arrangement enables the dots to be adequately formedwith the respective inks on a printing medium, so as to print an imageof high picture quality.

[0075] In accordance with one preferable application of the presentinvention, the printing apparatus creates dots with at least cyan ink,magenta ink, and yellow ink as the dots with the plurality of basiccolor inks.

[0076] The creation of dots with at least the cyan ink, the magenta ink,and the yellow ink enables expression of a practically sufficient numberof hues. The use of the dark ink in addition to these various color inksenhances the degree of freedom in specification of dot on-off conditionsand thereby improves the picture quality of the resulting printed image.

[0077] In accordance with another preferable application of the presentinvention, the printing apparatus creates dots with at least black inkin addition to the cyan ink, the magenta ink, and the yellow ink. Theprinting apparatus also creates dots with dark yellow ink, which has amain wavelength region of light absorption substantially identical withthat of the yellow ink but a lower lightness than that of the yellowink.

[0078] Creation of dots with the black ink in addition to the cyan ink,the magenta ink, and the yellow ink further improves the picture qualityof the resulting printed image. The use of the dark yellow ink inaddition to these inks enhances the degree of freedom in specificationof the dot on-off conditions and thereby improves the picture quality ofthe resulting printed image.

[0079] In accordance with another preferable application of the presentinvention, the printing apparatus creates dots with at least cyan ink,magenta ink, and yellow ink as the plurality of basic color inks, aswell as with the dark ink and at least one light ink, which has a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink.

[0080] Creation of dots with the variety of color inks including thelight ink improves the picture quality of the resulting printed image.The use of the dark ink in addition to these various color inks enhancesthe degree of freedom in specification of the dot on-off conditions andthereby further improves the picture quality of the resulting printedimage.

[0081] In accordance with sill another preferable application of thepresent invention, the printing apparatus creates at least twovariable-size dots having different sizes with regard to at least cyanink, magenta ink, and yellow ink as the plurality of basic color inks.

[0082] Creation of the at least two variable-size dots with regard tothe respective inks improves the picture quality of the resultingprinted image. The use of the dark ink in addition to these inksenhances the degree of freedom in specification of the dot on-offconditions and thereby further improves the picture quality of theresulting printed image.

[0083] In accordance with another preferable application of the presentinvention, the printing apparatus has an ink reservoir unit, in whichthe plurality of basic color inks and the dark ink are keptindependently.

[0084] In the printing apparatus having the ink reservoir unit forindependently keeping the plurality of basic color inks and the darkink, supplies of the respective inks from the ink reservoir unit to theprint head cause dots of the plurality of basic color inks and dots ofthe dark ink to be created on the printing medium. This results inprinting an image of high picture quality. The arrangement of keepingthe respective inks independently means that the respective inks shouldbe accommodated in a non-miscible manner. These inks may be kepttogether in one ink reservoir unit or may be kept separately indifferent ink reservoir unit.

[0085] In this printing apparatus, the ink reservoir unit may keep agreater quantity of the dark ink than a quantity of the one basic colorink corresponding to the dark ink.

[0086] When natural images, such as landscapes and portraits, areprinted, a greater quantity of the dark ink is generally consumed thanthe quantity of the basic color ink having the closest hue to that ofthe dark ink. The ink reservoir unit keeping the greater quantity of thedark ink than the quantity of the corresponding basic color ink thusfavorably causes the quantities of the respective inks kept in the inkreservoir unit to be close to the actual quantities of ink consumption.

[0087] In accordance with one preferable application of the printingapparatus of the present invention and the corresponding method ofprinting, the print head is driven according to the input controlinformation to create dots with the respective inks, wherein the controlinformation controls creation of dots with the plurality of basic colorinks, which include at least cyan ink, magenta ink, and yellow ink, aswell as with dark yellow ink, which has a main wavelength region oflight absorption substantially identical with that of the yellow ink buta lower lightness than that of the yellow ink.

[0088] In the printing apparatus of this arrangement and thecorresponding method of printing, dots are created with the dark yellowink as well as with the cyan ink, the magenta ink, and the yellow ink.This arrangement enhances the degree of freedom in specification of doton-off conditions and thereby improves the picture quality of theresulting printed image.

[0089] In accordance with one preferable application of the presentinvention, the printing apparatus has an ink reservoir unit that keepsat least the cyan ink, the magenta ink, the yellow ink, and the darkyellow ink independently. The ink reservoir unit keeps a greaterquantity of the dark yellow ink than a quantity of the yellow ink.

[0090] When natural images, such as landscapes and portraits, areprinted, a greater quantity of the dark yellow ink is generally consumedthan the quantity of the yellow ink. The ink reservoir unit keeping thegreater quantity of the dark yellow ink than the quantity of the yellowink thus favorably causes the quantities of the respective inks kept inthe ink reservoir unit to be close to the actual quantities of inkconsumption.

[0091] The technique of the present invention may be implemented by acomputer, which reads a specific program that actualizes the functionsof the printing system, the print controller, or the printing apparatusof the present invention discussed above. One application of the presentinvention is a recording medium, in which a specific program forattaining the functions of the printing system of the present inventionis recorded. The present invention is thus directed to a recordingmedium, in which a specific program is recorded in a computer readablemanner. The specific program actualizes a method of creating dots with aplurality of different inks, so as to print an image on a printingmedium. The specific program causes a computer to attain the functionsof: specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and controlling creation of dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot-on-off conditions with regard to the pluralityof basic color inks and the dark ink.

[0092] Another application of the present invention is a recordingmedium, in which a specific program for attaining the functions of theprint controller of the present invention is recorded. The presentinvention is thus directed to another recording medium, in which aspecific program is recorded in a computer readable manner. The specificprogram actualizes a method of supplying control information to aprinter, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof the printer. The specific program causes a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and a dark ink based on input image data,the plurality of basic color inks being combined with one another toexpress achromatic color, the dark ink having a main wavelength regionof light absorption substantially identical with that of one basic colorink selected out of the plurality of basic color inks but a lowerlightness than that of the selected basic color ink; and outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink to the printer as the controlinformation, so as to control the printing operation of the printer.

[0093] Still another application of the present invention is a recordingmedium, in which a specific program for attaining the functions of theprinting apparatus of the present invention is recorded. The presentinvention is thus directed to a recording medium, in which a specificprogram is recorded in a computer readable manner. The specific programactualizes a method of receiving control information to control creationof dots with a plurality of different inks and driving a print head,which creates dots with the plurality of different inks on a printingmedium, based on the control information, so as to print an image. Thespecific program causes a computer to attain the functions of: receivingthe control information to control creation of dots with a plurality ofbasic color inks and a dark ink, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and driving the print head based on the input controlinformation to create dots with the plurality of basic color inks andthe dark ink, thereby printing an image.

[0094] The computer reads any one of the specific programs recorded inthe recording media to actualize the respective functions. Creation ofdots with the dark ink as well as with the plurality of basic color inksimproves the picture quality of the resulting printed image.

[0095] In accordance with one preferable application of the presentinvention, the specific program recorded in the recording medium forattaining the functions of the print controller further causes thecomputer to attain the function of storing in advance mappings of tintsused to express a color image to combinations of the plurality of basiccolor inks and the dark ink to represent the tints. In this structure,the dot on-off conditions with regard to the plurality of basic colorinks and the dark ink are specified, based on the mappings stored inadvance. This arrangement ensures the quick and accurate specificationof the dot on-off conditions.

[0096] The plurality of basic color inks generally include the cyan ink,the magenta ink, and the yellow ink. It is preferable that the dark inkhas a hue close to the hue of the yellow ink, which has the highestlightness among these basic color inks. There is accordingly anotherpossible application of the recording medium, in which a specificprogram for attaining the functions of the print controller is recorded.The present invention is thus directed to a recording medium, in which aspecific program is recorded in a computer readable manner. The specificprogram actualizes a method of supplying control information to aprinter, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof the printer. The specific program causes a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and dark yellow ink based on input imagedata, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; andoutputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark yellow ink to the printeras the control information, so as to control the printing operation ofthe printer.

[0097] There is also another possible application of the recordingmedium, in which a specific program for attaining the functions of theprinting apparatus is recorded. The present invention is thus directedto a recording medium, in which a specific program is recorded in acomputer readable manner. The specific program actualizes a method ofreceiving control information to control creation of dots with aplurality of different inks and driving a print head, which creates dotswith the plurality of different inks on a printing medium, based on thecontrol information, so as to print an image. The specific programcauses a computer to attain the functions of: receiving the controlinformation to control creation of dots with a plurality of basic colorinks and dark yellow ink, the plurality of basic color inks including atleast cyan ink, magenta ink, and yellow ink, the dark yellow ink havinga main wavelength region of light absorption substantially identicalwith that of the yellow ink but a lower lightness than that of theyellow ink; and driving the print head based on the input controlinformation to create dots with the plurality of basic color inks andthe dark yellow ink, thereby printing an image.

[0098] The computer reads the specific program recorded in the recordingmedium to actualize the respective functions, so as to create dots withat least the cyan ink, the magenta ink, the yellow ink, and the darkyellow ink. This arrangement enables an image of high picture quality tobe printed.

[0099] In the printing apparatus of the present invention, the dark inkis supplied by the dark ink supply unit. Other possible applications ofthe present invention are accordingly ink cartridges, in which th darkis kept. The present invention is thus directed to an ink cartridgedetachably attached to a printing apparatus, which prints an image witha plurality of basic color inks, wherein the plurality of basic colorinks are combined with one another to express achromatic color. The inkcartridge keeps therein at least one ink to be supplied to the printingapparatus. The ink cartridge has an ink reservoir that keeps therein adark ink, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink.

[0100] Attachment of this ink cartridge to the printing apparatusenables the printing apparatus to create dots with the dark ink. Asdescribed previously, this arrangement enhances the degree of freedom inspecification of the dot on-off conditions and improves the picturequality of the resulting printed image.

[0101] In accordance with one preferable application of the presentinvention, the dark ink kept in the ink cartridge has lower lightnessand saturation than those of one basic color ink selected out of theplurality of basic color inks.

[0102] In accordance with another preferable application of the presentinvention, the dark ink kept in the ink cartridge has a main wavelengthregion for most strongly absorbing a ray in a visible range, which issubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks, and a greater integral of lightabsorptivity in a wavelength region of the visible range than that ofthe selected basic color ink.

[0103] In accordance with still another preferable application of thepresent invention, the dark ink kept in the ink cartridge has:

[0104] (A) a characteristic wavelength region for strongly absorbing aray in a visible range to mainly determine the hue of the dark ink,which is substantially identical with a characteristic wavelength regionof one basic color ink selected out of the plurality of basic colorinks;

[0105] (B) a mean value of light absorptivity that is greater than orsubstantially identical with a mean value of light absorptivity of theselected basic color ink in the characteristic wavelength region of thedark ink; and

[0106] (C) a mean value of light absorptivity that is greater than amean value of light absorptivity of the selected basic color ink in awavelength region of visible light except the characteristic wavelengthregion of the dark ink.

[0107] Attachment of the ink cartridge, in which any one of these darkinks is kept, to the printing apparatus enables the printing apparatusto create dots with the dark ink. This arrangement improves the picturequality of the resulting printed image.

[0108] In accordance with one preferable application of the presentinvention, the ink cartridge further keeps therein one basic color inkselected out of the plurality of basic color inks. In accordance withanother preferable application of the present invention, the inkcartridge further keeps therein black ink, which is achromatic and has alow lightness. In accordance with still another preferable applicationof the present invention, the ink cartridge further keeps therein atleast one light ink, which has a hue substantially identical with thatof at least one basic color ink selected out of the plurality of basiccolor inks but a lower density than that of the at least one basic colorink.

[0109] The arrangement of keeping any of these inks in addition to thedark ink in the same ink cartridge saves the total space required forthe ink cartridges, compared with separate ink cartridges thatindependently keep one of these inks therein.

[0110] In accordance with another preferable application of the presentinvention, the ink cartridge further keeps therein one basic color inkselected out of the plurality of basic color inks and at least one lightink, which has a hue substantially identical with that of at least onebasic color ink selected out of the plurality of basic color inks but alower density than that of the at least one basic color ink. Thearrangement of keeping these inks together in addition to the dark inkin the same ink cartridge further saves the total space required for theink cartridges. These color inks including the dark ink are mainlyconsumed in the process of printing a color image, whereas the black inkis mainly consumed in the process of printing a black and white image,for example, a document. The arrangement keeps these color inks, whichare mainly consumed to print a color image, together in the same inkcartridge, separate from the black ink. This arrangement desirablyenables only the ink cartridge keeping inks mainly consumed to bereplaced according to the image to be printed.

[0111] The ink cartridg of the present invention may keep therein an inkhaving the following characteristics as the dark ink:

[0112] (A) a characteristic wavelength region that is mostly in awavelength range of 400 nm to 500 nm, the characteristic wavelengthregion strongly absorbing a ray in a visible range to mainly determinethe hue of the dark yellow ink; and

[0113] (B) a mean value of absorptivity of the ray in the visible rangeexcept the characteristic wavelength region, which ranges from 10% to60%.

[0114] The ink cartridge of the present invention may alternatively keeptherein an ink having the following characteristics as the dark ink:

[0115] (A) a hue included in a specific range of 10R to 10GY on aMunsell hue circle; and

[0116] (B) a saturation of smaller than 3.5C on a Munsell chroma.

[0117] Attachment of the ink cartridge, in which any of these inks iskept, to the printing apparatus enables the printing apparatus to createdots with the dark ink. This arrangement improves the picture quality ofthe resulting printed image.

[0118] The present invention is directed to an ink cartridge that keepstherein yellow ink and dark yellow ink, which has a lower lightness thanthat of the yellow ink. The present invention is also directed to an inkcartridge that keeps therein dark yellow ink and black ink. The presentinvention is further directed to an ink cartridge that keeps thereinyellow ink, dark yellow ink, cyan ink, light cyan ink, magenta ink, andlight magenta ink.

[0119] The arrangement of keeping these inks together in the same inkcartridge saves the total space required for the ink cartridges,compared with separate ink cartridges that independently keep one ofthese inks therein.

[0120] In accordance with one preferable application of the inkcartridge, the capacity of the dark yellow ink may be set to be greaterthan the capacity of the yellow ink. When a natural image, such as alandscape or a portrait, is printed, the consumption of the dark yellowink tends to be greater than the consumption of the yellow ink. Thegreater capacity of the dark yellow ink than that of the yellow ink thusenables these two inks to be used up at substantially the same time.This arrangement desirably reduces the waste of ink by a replacement ofthe ink cartridge, in which one ink is used up but a large quantity ofthe other ink still remains.

[0121] The present invention is also directed to an ink cartridge thatkeeps therein dark yellow ink, light cyan ink and light magenta ink. Thearrangement of keeping these inks together in the same ink cartridgesaves the total space required for the ink cartridges, compared withseparate ink cartridges that independently keep one of these inkstherein. When a natural image, such as a landscape or a portrait, isprinted, these inks are often consumed more than the other inks. Thearrangement of keeping the dark yellow ink the light cyan ink, and thelight magenta ink in the same ink cartridge enables only this inkcartridge to be replaced according to the image to be printed.

[0122] In accordance with one preferable application of the presentinvention, the ink cartridge further has a storage device that storesinformation regarding a quantity of each ink kept therein in a readable,writable, and volatile manner.

[0123] Storing the information regarding the quantity of each ink keptin the ink cartridge ensures the printing operation based on theinformation with regard to the accurate remaining quantity of ink. Thisarrangement effectively prevents the ink from being used up in thecourse of printing.

[0124] The storage device included in the ink cartridge may have an inkquantity information storage area, which is accessed to be written firstby the printing apparatus and in which the information regarding thequantity of each ink kept in the ink cartridge is stored.

[0125] The area written first is, for example, a head area in thestorage device or any area in the storage device accessible to bewritten first by the printing apparatus. Storing the informationregarding the quantity of each ink in this area shortens the timerequired for writing the information. This arrangement effectivelyprevents the information to be written from being destroyed by cuttingoff the power supply of the printing apparatus in the course of thewriting operation.

[0126] When the dark ink kept in the ink cartridge is used up, an inksupplier is used to feed a supply of the dark ink to the ink cartridge,so as to continue creation of dots with the dark ink and print an imageof high quality. Another application of the present invention isaccordingly an ink supplier. The present invention is thus directed toan ink supplier that feeds a supply of ink to an ink cartridge, whereinthe ink cartridge is detachably attached to a printing apparatus andkeeps therein at least one ink used by the printing apparatus. The inksupplier includes a sealed ink reservoir that keeps an ink in a sealingmanner, and an ink supply unit that feeds a supply of the sealed ink tothe ink cartridge. The ink sealed in the sealed ink reservoir has thefollowing characteristics:

[0127] (A) a characteristic wavelength region that is mostly included ina wavelength range of 400 nm to 500 nm, the characteristic wavelengthregion ,strongly absorbing a ray in a visible range to mainly determinethe hue of the ink; and

[0128] (B) a mean value of absorptivity of the ray in the visible rangeexcept the characteristic wavelength region, which ranges from 10% to60%.

[0129] The ink supplier has the sealed ink reservoir that keeps an inkin a sealing manner, and the ink supply unit that feeds a supply of thesealed ink to the ink cartridge. The ink having the abovecharacteristics (A) and (B) is sealed in the sealed ink reservoir. Thecharacteristic wavelength region of the ink, which mainly determines thehue of the ink, is mostly included in the wavelength range of 400 nm to500 nm. This means that the ink roughly has the hue of yellow. The inkhas the mean value of absorptivity of the ray in the visible rangeexcept the characteristic wavelength region, which ranges from 10% to60%. This means that the ink has a low lightness. The ink having thecharacteristics (A) and (B) is accordingly replaceable with the darkink. In the event that the dark ink kept in the ink cartridge is usedup, supply of the ink from the ink supplier to the ink cartridge enablescontinuous creation of dots with the dark ink to print an image of highpicture quality.

[0130] The ink sealed in the ink supplier may alternatively have thefollowing characteristics:

[0131] (A) a hue included in a specific range of 10R to 10GY on aMunsell hue circle; and

[0132] (B) a saturation of smaller than 3.5C on a Munsell chroma.

[0133] This ink may also be used as the dark ink. A supply of this inksealed in the ink supplier to the ink cartridge enables creation of dotswith the dark ink.

[0134] The technique of the present invention may be implemented by aprogram code that is stored in a computer to attain the functions of theprinting system, the print controller, or the printing apparatus of thepresent invention discussed above. The computer then executes therespective functions written in the program code. A first possibleapplication of the present invention is thus a program code, in which amethod of creating dots with a plurality of different inks so as toprint an image on a printing medium is written in a computer readablemanner. The method actualizes the functions of: specifying dot on-offconditions with regard to a plurality of basic color inks and a dark inkbased on input image data, the plurality of basic color inks beingcombined with one another to express achromatic color, the dark inkhaving a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and controlling creation of dots with the plurality ofbasic color inks and the dark ink, based on the specification of thedot-on-off conditions with regard to the plurality of basic color inksand the dark ink.

[0135] A second possible application of the present invention is aprogram code, in which a method of supplying control information to aprinter, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof the printer is written in a computer readable manner. The methodactualizes the functions of: specifying dot on-off conditions withregard to a plurality of basic color inks and a dark ink based on inputimage data, the plurality of basic color inks being combined with oneanother to express achromatic color, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; andoutputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to the printer as thecontrol information, so as to control the printing operation of theprinter.

[0136] A third possible application of the present invention is aprogram code, in which a method of receiving control information tocontrol creation of dots with a plurality of different inks and drivinga print head, which creates dots with the plurality of different inks ona printing medium; based on the control information, so as to print animage is written in a computer readable manner. The method actualizesthe functions of: receiving the control information to control creationof dots with a plurality of basic color inks and a dark ink, theplurality of basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; and driving the print headbased on the input control information to create dots with the pluralityof basic color inks and the dark ink, thereby printing an image.

[0137] Any of the print controllers and the printing apparatuses of thepresent invention discussed above may provide a plurality of dark inksand uses a most suitable dark ink or the plurality of dark inkssimultaneously according to an image to be printed. The presentinvention may accordingly have other possible applications discussedbelow. A fourth possible application of the present invention is thus aprint controller that supplies control information to a printer, whichcreates dots with a plurality of different inks, in order to control thecreation of dots with the plurality of different inks. The printercreates dots with a plurality of basic color inks as well as with aplurality of dark inks, wherein the plurality of basic color inks arecombined with one another to express achromatic color, and each of thedark inks has a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink. The print controller includes: a dot on-off conditionspecification unit that specifies dot on-off conditions with regard tothe plurality of basic color inks and the plurality of dark inks, basedon input image data; and a control information output unit that outputsthe specification of the dot on-off conditions with regard to theplurality of basic color inks and the plurality of dark inks to theprinter as the control information.

[0138] A fifth possible application of the present invention is aprinting apparatus that has a print head to create dots with a pluralityof different inks on a printing medium, receives control information tocontrol the creation of dots with the plurality of different inks, andactually creates dots with the plurality of different inks, based on theinput control information, so as to print an image. The printingapparatus includes: a basic color ink supply unit that supplies aplurality of basic color inks to the print head, wherein the pluralityof basic color inks are combined with one another to express achromaticcolor; a dark ink supply unit that supplies a plurality of dark inks tothe print head, wherein each of the dark inks has a main wavelengthregion of light absorption substantially identical with that of onebasic color ink selected out of the plurality of basic color inks but alower lightness than that of the selected basic color ink; a controlinformation input unit that receives the control information with regardto dots of the plurality of basic color inks and the plurality of darkinks; and a dot formation unit that drives the print head based on theinput control information, so as to create dots with the plurality ofbasic color inks and the plurality of dark inks.

[0139] These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiment with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0140]FIG. 1 is a block diagram schematically illustrating the structureof a printing system including a print controller and a color printer inone embodiment according to the present invention;

[0141]FIG. 2 is a block diagram illustrating a software configuration ofthe printing system of the embodiment;

[0142]FIG. 3 schematically illustrates the structure of the colorprinter of the embodiment;

[0143]FIGS. 4A and 4B show the principle of dot formation in the colorprinter of the embodiment;

[0144]FIGS. 5A and 5B show arrangements of nozzles in the color printerof the embodiment;

[0145]FIG. 6 shows the internal structure of the print controller of theembodiment;

[0146]FIG. 7 shows a process of receiving data output from a print headto a drive buffer and creating dots in the printing system of theembodiment;

[0147]FIGS. 8A through 8F are perspective views showing ink cartridgesattachable to the color printer of the embodiment;

[0148]FIGS. 9A and 9B are graphs showing observed quantities of inkconsumption when natural images are printed with the color printer ofthe embodiment;

[0149]FIG. 10 is an enlarged view illustrating a storage element mountedon the side face of the ink cartridge;

[0150]FIG. 11 shows the contents of data stored in the storage elementof the ink cartridge;

[0151]FIG. 12 shows an example of ink compositions used in the colorprinter of the embodiment;

[0152]FIG. 13 is a graph showing the curves of lightness with regard tothe respective inks having the compositions shown in FIG. 12;

[0153]FIGS. 14A through 14E are graphs conceptually showing thespectroscopic characteristics of the respective color inks used in thecolor printer of the embodiment;

[0154]FIG. 15 is a graph showing the spectroscopic characteristics ofdark yellow ink that is designed by utilizing the degree of freedom inspectroscopic settings in a wavelength region of longer than 650 nm;

[0155]FIG. 16 shows expression of colors with dots of dark yellow ink ona sheet of printing paper;

[0156]FIG. 17 schematically illustrates the appearance of an inksupplier used to feed a supply of ink to the ink cartridge;

[0157]FIG. 18 is a flowchart showing an image processing routineexecuted in the embodiment;

[0158]FIG. 19 shows a conversion table used in the embodiment;

[0159]FIGS. 20A and 20B conceptually show a method of determining therate of formation of dark ink dots in the embodiment;

[0160]FIGS. 21A and 21B show a binarization process;

[0161]FIG. 22 is a flowchart showing a binarization process by the errordiffusion method executed in the embodiment;

[0162]FIG. 23 shows an example of weights added in the process ofdiffusing the error by the error diffusion method;

[0163]FIG. 24 shows the systematic dither method;

[0164]FIGS. 25A, 25B, and 25C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black with the color printer ofthe embodiment;

[0165]FIGS. 26A, 26B, and 26C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black with the colorprinter of the embodiment;

[0166]FIGS. 27A, 27B, and 27C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from white to black with the color printerof the embodiment;

[0167]FIGS. 28A, 28B, and 28C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black with the color printerusing only the four color inks C, M, Y, and K; and

[0168]FIGS. 29A and 29B show results of simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from white to black with the color printerusing only the three color inks C, M, and Y.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0169] One mode for carrying out the present invention is describedbelow in the following sequence as a preferred embodiment:

[0170] A. Structure of Apparatus

[0171] A-1. General Structure

[0172] A-2. Structure of Ink Cartridge

[0173] A-3. Dark Yellow Ink

[0174] B. Image Processing

[0175] B-1. Process of Converting Resolution

[0176] B-2. Color Conversion Process

[0177] B-3. Process of Converting Number of Tones

[0178] B-4. Binarization by Error Diffusion Method

[0179] B-5. Binarization by Systematic Dither Method

[0180] B-6. Interlace Process

[0181] C. Results of Simulations

[0182] C-1. Gradation Pattern from Red to Black

[0183] C-2. Gradation Pattern from Magenta to Black

[0184] C-3. Gradation Pattern from White to Black

[0185] C-4. Application to Printer with Four Color Inks

[0186] C-5. Application to Printer with Three Color Inks

[0187] A. Structure of Apparatus

[0188] A-1. General Structure

[0189]FIG. 1 is a block diagram schematically illustrating the structureof a printing system including a print controller and a printingapparatus in one embodiment according to the present invention. FIG. 2is a block diagram illustrating a software configuration of the printingsystem of the embodiment. The printing system includes a computer 80connected to a color printer 20 and a color scanner 21. The computer 80reads and executes predetermined programs to function, in combinationwith the color printer 20 and the color scanner 21, as the printingsystem as a whole. The color scanner 21 converts a color original, thatis, an object to be printed, into color image data ORG, which are in aprocessible form by the computer 80 and input into the computer 80. Thecomputer 80 carries out required image processing and further convertsthe color image data ORG into image data FNL, which are in a printableform by the printer 20 and input into the color printer 20. The imagedata processible by the computer 80 include those representing imagesread by the color scanner 21 with or without subsequent processing, aswell as those representing images generated by a variety of applicationprograms 91 on the computer 80. The color printer 20 creates dots ofvarious color inks on a sheet of printing paper based on the input imagedata FNL. The series of this procedure enables a resulting color imagecorresponding to the color image data output from the computer 80 to beprinted on the printing paper.

[0190] The computer 80 includes a CPU 81 that carries out a variety ofoperations, a ROM 82, a RAM 83, an input interface 84, an outputinterface 85, a CRT controller (CRTC) 86, a disk controller (DDC) 87,and a serial input-output interface (SIO) 88, which are mutuallyconnected via a bus 89 to allow transmission of data. The CRTC 86controls output of signals to a color display CRT 23. The DDC 87controls data transmission to and from a flexible disk drive 25, a harddisk 26, and a CD-ROM drive (not shown). A variety of programs loaded tothe RAM 83 and executed by the CPU 81 and a variety of programs providedin the form of device drivers are stored in the ROM 82 and the hard disk26. Connection of the SIO 88 with a public telephone network PNT via amodem 24 enables required data and programs to be downloaded to the harddisk 26 from a serer SV on an external network.

[0191] A supply of power to the computer 80 activates the operatingsystem stored in the ROM 82 and the hard disk 26 and a variety ofapplication programs 91 under the control of the operating system.

[0192] The color printer 20 of this embodiment is a color ink jetprinter that forms dots of seven different color inks, that is, cyan,light cyan, magenta, light magenta, yellow, dark yellow, and black inks,on a sheet of printing paper and thereby prints a color image. The inkjet printer applied in this embodiment uses piezoelectric elements PE toeject ink as discussed later. The printer may, however, have a printhead that ejects ink by another technique, for example, by means ofbubbles that are generated in an ink conduit by a supply of electricityto a heater disposed in the ink conduit.

[0193] In color printers driven by other principles, for example, laserprinters and thermal transfer printers, there is no fear of tearing orrumpling the printing medium. Application of a large quantity of ink onthe printing medium may, however, cause problems of ink blot andpeel-off. The technique of the embodiment discussed below may thus beapplicable to such color printers.

[0194] Referring to FIG. 2, in the computer 80, all the applicationprograms 91 work under the control of the operating system. A videodriver 90 and a printer driver 92 are incorporated in the operatingsystem, and image data output from each application program 91 areoutput to the color printer 20 via the printer driver 92. Theapplication program 91 that processes an input image, for example, byretouch causes the input image taken from the color scanner 21 to bedisplayed on the CRT 23 via the video driver 90. This enables the userto carry out the required image processing while checking the displayedimage on the CRT 23.

[0195] When the application program 91 issues a print instruction, theprinter driver 92 of the computer 80 receives image data from theapplication program 91 and carries out predetermined image processing toconvert the input image data to image data FNL that are printable by theprinter 20. As shown conceptually in FIG. 2, the image processingcarried out in the printer driver 92 is mainly classified into fourmodules, that is, a resolution conversion module 93, a color conversionmodule 94, a halftone module 95, and an interlace module 96. The detailsof the image processing carried out by each module will be discussedlater. The image data received by the printer driver 92 are subjected tothe image processing performed by the respective modules and are outputas the final image data FNL to the color printer 20. The color printer20 of this embodiment does not carry out the image processing but simplycreates dots according to the input image data FNL. A modifiedapplication may, however, cause the color printer 20 to carry out partof the image processing.

[0196]FIG. 3 schematically illustrates the structure of the colorprinter 20 in this embodiment. The color printer 20 has a mechanism ofdriving a print head 41 mounted on a carriage 40 to implement inkejection and dot creation, a mechanism of moving the carriage 40 forwardand backward along an axis of a platen 36 by means of a carriage motor30, a mechanism of feeding a sheet of printing paper P by means of asheet feed motor 35, and a control circuit 60. The mechanism ofreciprocating the carriage 40 along the axis of the platen 36 includes asliding shaft 33 that slidably holds the carriage 40 arranged inparallel with the axis of the platen 36, a pulley 32 that is linked withthe carriage motor 30 via an endless drive belt 31 spanned therebetween,and a position sensor 34 that detects the position of the origin of thecarriage 40. The mechanism of feeding the printing paper P includes theplaten 36, the sheet feed motor 35 that rotates the platen 36, asheet-feed assist roller (not shown), and a gear train (not shown) thattransmits the rotation of the sheet feed motor 35 to the platen 36 andthe sheet-feed assist roller. The control circuit 60 transmits signalsto and from a control panel 59 of the printer 20 and adequately controlsthe operations of the sheet feed motor 35, the carriage motor 30, andthe print head 41. The sheet of printing paper P fed to the colorprinter 20 is held between the platen. 36 and the sheet-feed assistroller and fed by a predetermined length according to a rotational angleof the platen 36.

[0197] Ink cartridges 42 and 43 are detachably attached to the carriage40. In one example, the ink cartridge 42 has only black (K) ink kepttherein, whereas the ink cartridge 43 has a total of six different colorinks, three basic color inks, that is, cyan (C), magenta (M), and yellow(Y) inks, as well as three additional color inks, that is, light cyan(LC), light magenta (LM), and dark yellow (DY) inks, kept therein.Namely the color printer 20 has dark ink in addition to the standard inkwith regard to yellow, and light ink in addition to the standard inkwith regard to cyan and magenta.

[0198] The combination of these inks may be changed. For example, thedark-yellow (DY) ink, the light cyan (LC) ink, and the light magenta(LM) ink may be kept in one ink cartridge. In another example, only thedark yellow (DY) ink may be kept in a separate ink cartridge. Thestructures of these ink cartridges will be discussed in detail later.

[0199] The ink cartridge 43 has a storage element 52 (see FIG. 6), inwhich pieces of information, for example, with regard to the remainingquantities of the respective inks, are stored. The storage element 52has an EEPROM. The computer 80 writes and reads the data regarding theremaining quantities of inks into and from the storage element 52 viathe control circuit 60 of the color printer 20. The details of theprocess of reading and writing the data regarding the remainingquantities of inks will be discussed later.

[0200] The print head 41 disposed on the lower portion of the carriage40 has ink ejection heads 44, 45, 46, 47, 48, 49, 50 that respectivelycorrespond to the K, C, LC, M, LM, Y, and DY inks. Ink supply conduits(not shown) are formed for the respective inks in the bottom of thecarriage 40. When the ink cartridges 42 and 43 are attached to thecarriage 40, the respective inks kept in the ink cartridges 42 and 43are supplied to the ink ejection heads 44 through 50 via thecorresponding ink supply conduits. The supply of ink fed to each of theink ejection heads 44 through 50 is ejected from the print head 41 tocreate dots on the printing paper P according to the technique discussedbelow.

[0201]FIG. 4A shows the internal structure of the print head 41. Fortyeight nozzles Nz are formed in each of the ink ejection heads 44 through50 corresponding to the respective colors. Each nozzle has an inkconduit 51 and a piezoelectric element PE arranged on the ink conduit51. As is known by those skilled in the art, the piezoelectric elementPE deforms its crystal structure by application of a voltage andimplements an extremely high-speed conversion of electrical energy intomechanical energy. In this embodiment, when a preset voltage is appliedbetween electrodes on either end of the piezoelectric elements PE for apredetermined time period, the piezoelectric element PE is expanded forthe predetermined time period to deform one side wall of the ink conduit51 as shown in FIG. 4B. The volume of the ink conduit 51 is reducedaccording to the expansion of the piezoelectric element PE. A certainquantity of ink corresponding to the reduction is ejected as an inkparticle Ip from the nozzle Nz at a high speed. The ink particle Ipsoaks into the printing paper P set on the platen 36 and creates a doton the printing paper P.

[0202]FIGS. 5A and 5B show possible arrangements of ink jet nozzles Nzon the ink ejection heads 44 through 50. In the example of FIG. 5A, onlythe black (K) ink is kept in the ink cartridge 42, whereas the sixdifferent color inks, that is, cyan (C), magenta (M), yellow (Y), lightcyan (LC), light magenta (LM), and dark yellow (DY) inks, are kept inthe ink cartridge 43. Accommodation of a plurality of different inks inone ink cartridge desirably reduces the required number of inkcartridges and the total space required for attachment of the inkcartridges. In another example as shown in FIG. 5B, the DY ink may bekept with the LC and LM inks in the same ink cartridge. In still otherexamples, the DY ink may be kept with the C, M, and Y inks or with the Kink.

[0203] As shown in FIG. 5A, seven nozzle arrays, from which therespective color inks are ejected, are formed in the bottom faces of therespective ink ejection heads 44 through 50. Each nozzle array includesforty eight nozzles Nz arranged in zigzag at a preset nozzle pitch k.The forty eight nozzles Nz included in each nozzle array may be arrangedin alignment, instead of in zigzag. The zigzag arrangement shown in FIG.5A, however, has an advantage that the nozzle array can be designed tohave a small nozzle pitch k.

[0204] Referring to FIG. 5A, the ink ejection heads 44 through 50 of therespective colors are shifted in position in the moving direction of thecarriage 40. Since the nozzles included in each ink ejection head arearranged in zigzag, the nozzles are also shifted in position in themoving direction of the carriage 40. The control circuit 60 of the colorprinter 20 drives the respective ink ejection heads 44 through 50 atsuitable head drive timings by taking into account the positionaldifferences of the nozzles in the course of moving the carriage 40 anddriving the nozzles.

[0205]FIG. 6 illustrates the internal structure of the control circuit60 in the color printer 20. The control circuit 60 includes a CPU 61, aPROM 62, a RAM 63, a PC interface 64 that transmits data to and from thecomputer 80, a peripheral equipment input-output unit (PIO) 65 thattransmits data to and from the sheet feed motor 35, the carriage motor30, and other elements, a timer 66, and a drive buffer 67. The dataregarding the remaining quantities of inks or the quantities ofconsumption of inks are read from or written into the storage element 52incorporated in the ink cartridge 43 via the PIO 65. The drive buffer 67functions to supply dot on/off signals to the ink ejection heads 44through 50. These elements are mutually connected via a bus 68 to allowtransmission of data. The control circuit 60 further includes anoscillator 70 that outputs driving waveforms at selected frequencies anda distributor 69 that distributes the outputs from the oscillator 70 tothe ink ejection heads 44 through 50 at specified timings.

[0206] The control circuit 60 constructed as shown in FIG. 6 receivesthe image data FNL output from the computer 80 and temporarily storesthe dot on/off signals in the RAM 63. The CPU 61 outputs the dot data tothe drive buffer 67 at preset timings synchronously with the operationsof the sheet feed motor 35 and the carriage motor 30.

[0207] The following describes a mechanism of creating dots in responseto the dot on/off signals output from the CPU 61 to the drive buffer 67.FIG. 7 illustrates connection of one nozzle array in the ink ejectionheads 44 through 50. The nozzle array in each of the ink ejection heads44 through 50 is included in a circuit, in which the drive buffer 67works as the source and the distributor 69 as the sink. Thepiezoelectric elements PE corresponding to the nozzles Nz included inthe nozzle array have one electrodes respectively connected to therespective output terminals of the drive buffer 67 and the otherelectrodes collectively connected to the output terminal of thedistributor 69. The driving waveforms of the oscillator 70 are outputfrom the distributor 69 as shown in FIG. 7. When the CPU 61 outputs thedot on/off signals of the respective nozzles to the drive buffer 67,only the piezoelectric elements PE receiving the ON signal are driven inresponse to the output driving waveforms. The ink particles Ip are thusejected from the nozzles corresponding to the piezoelectric elements PEthat have received the ON signal from the drive buffer 67.

[0208] The color printer 20 having the hardware configuration discussedabove drives the carriage motor 30 to move the ink ejection heads 44through 50 of the respective colors relative to the printing paper P inthe main scanning direction, and drives the sheet feed motor 35 to shiftthe printing paper P in a sub-scanning direction. Under the control ofthe control circuit 60, the print head 41 is driven at adequate timingswhile the main scans and sub-scans of the carriage 40 are repeated. Thecolor printer 20 accordingly prints a color image on the printing paperP.

[0209] A-2. Structure of Ink Cartridge

[0210]FIG. 8A shows the appearance of the ink cartridge 43 attached tothe color printer 20 of this embodiment. As mentioned previously, theink cartridge 43 has the total of six different color inks, that is,cyan (C), light cyan (LC), magenta (M), light magenta (LM), yellow (Y),and dark yellow (DY) inks, kept therein. Accommodation of a plurality ofdifferent inks in one ink cartridge desirably reduces the requirednumber of ink cartridges and the total space required for the attachmentof ink cartridges. The ink cartridge 43 has the storage element 52including the EEPROM, in which various pieces of information are storedas discussed later.

[0211] The quantities of the respective color inks kept in the inkcartridge 43 are determined according to the expected quantities of useof the respective color inks, so as to satisfy the following relations.The quantity of the DY ink is set greater than the quantity of the Yink. The quantity of the LC ink is set greater than the quantity of theC ink. The quantity of the LM ink is set greater than the quantity ofthe M ink. The arrangement of setting the quantities of inks kept in oneink cartridge according to the expected quantities of use of therespective inks enables all the color inks to be used up atsubstantially the same time. Namely this arrangement reduces the wasteof ink.

[0212]FIGS. 9A and 9B are graphs showing observed quantities of inkconsumption when natural images, such as landscapes and portraits, areprinted with the color printer 20 of the embodiment. The consumedquantities of the respective color inks are varied to some extent by avariety of settings in the color printer 20 as described later. Theexpected quantities of use of the respective color inks can, however, beroughly specified by such observed values.

[0213]FIG. 9A shows the mean consumed quantities of the respective colorinks with regard to typical nine images including landscapes andportraits. In the graphs of FIGS. 9A and 9B, the consumed quantity ofeach color ink is shown as a relative value to a predetermined referencevalue. FIG. 9B shows the consumed quantities of the respective colorinks when an N1 sample image is printed out of high definition colordigital standard image data (ISO/JIS-SCID). The high definition colordigital standard image data are supplied in the form of CMY image data,so that the input image data are converted to RGB image data and outputto the color printer 20 for printing.

[0214] The curves of dotted line in both FIGS. 9A and 9B represent theobserved quantities of ink consumption with the color printer that doesnot use the DY ink but uses only six inks, C, LC, M, LM, Y, and K. Sincethe natural images generally have a large fraction of medium tones, thegreater quantities of the lighter inks, that is, the LC, LM, and Y inks,are used to print the natural images. The DY ink has a color that issimilar to a mixture of the Y, LC, and LM inks as described later. Thesimilar images can thus be printed by creating dots of the DY ink,instead of creating dots of the Y ink, the LC ink, and the LM ink. Thecurves of solid line in both FIGS. 9A and 9B represent the observedquantities of ink consumption when the DY ink as well as the other inksare used to print an image. The ratio of replacement of the Y dots, theLC dots, and the LM dots with the DY dots may be varied according to thecomposition of the DY ink and the usage of the DY dots as discussedlater. The rough tendency is, however, understood from the measurementresults shown in FIGS. 9A and 9B.

[0215] As clearly understood from the measurement results of FIGS. 9Aand 9B, when a natural image is printed using the DY dots, theconsumption of the DY ink tends to be greater than that of the Y ink(see the curves of solid line in FIGS. 9A and 9B). As mentionedpreviously, a large number of the Y dots, the LC dots, and the LM dotsare created to print a natural image without using the DY dots (see thecurves of dotted line in FIGS. 9A and 9B). The use of the DY ink enablesa large portion of the Y dots, the LC dots, and the LM dots to bereplaceable with the DY dots. In the measurement results of FIGS. 9A and9B, the consumption of the DY ink is approximately double theconsumption of the Y ink.

[0216] As in the case without the DY dots, in the case with the DY dots,the consumption of the LC ink tends to be greater than that of the C inkand the consumption of the LM ink tends to be greater than that of the Mink. Formation of the DY dots enables reduction of the number of the LCdots and the LM dots and thereby ensures a certain margin for therestriction of ink duty. The C dots and the M dots are accordinglyreplaced with the more inconspicuous LC dots and the LM dots. Thisresults in reducing the number of the C dots and the M dots, while notsignificantly varying the total number of the LC dots and the LM dots.In the case with the DY dots, the consumption of the LC ink is thusgreater than the consumption of the C ink, and the consumption of the LMink is greater than the consumption of the M ink.

[0217] As shown in FIG. 8, the ink cartridge 43 of the embodiment has agreater capacity of the DY ink than that of the Y ink, a greatercapacity of the LC ink than that of the C ink, and a greater capacity ofthe LM ink than that of the M ink. Namely the quantities of inks kept inthe ink cartridge 43 substantially correspond to the observed quantitiesof consumption of the respective color inks shown in FIGS. 9A and 9B.This effectively prevents the waste of inks kept in the ink cartridge.

[0218] As described previously, in the color printer 20 of theembodiment, the K ink is kept in the ink cartridge 42, whereas the sixcolor inks other than the K ink are kept in the ink cartridge 43. Thecombination of the color inks kept in the ink cartridge is, however, notrestricted to this embodiment, but may be any one of the combinationsshown in FIGS. 8B through 8F. In the examples of FIGS. 8B through 8F,the storage element 52 is omitted from the illustration. This does notmean that only the ink cartridge 43 shown in FIG. 8A has the storageelement 52 but the other ink cartridges do not have the storage element52.

[0219] In the case where only the DY ink alone is kept in an inkcartridge as shown in. FIG. 8B, there is no necessity of replacing theink cartridge until the DY ink is completely used up. This arrangementperfectly prevents any waste of the DY ink. Since the consumption of theDY ink is greater than the consumption of the Y ink, it is preferable toset the capacity of the DY ink greater than the capacity of the Y ink.This prevents the frequent replacement of the ink cartridge of the DYink. The ink cartridge with the only DY ink alone kept therein isattachable to the color printer having a monochromatic ink cartridge,for example, an ink cartridge for black ink. Using a special printerdriver for the DY ink available alone or with the ink cartridge of theDY ink enables creation of the DY dots even in the color printer thathas been designed without any consideration of the DY ink. Creation ofthe DY dots enables an image of high picture quality to be printed,because of the reasons discussed later.

[0220] In another example shown in FIG. 8C, the three color inks, DY,LC, and LM inks, are kept in one ink cartridge, whereas the other fourcolor inks C, M, Y, and K may be kept together in another ink cartridgeor only the K ink alone may be kept in another ink cartridge separatelyfrom still another ink cartridge of the C, M, and Y inks. Thearrangement of keeping the three color inks, DY, LC, and LM inks, whichare used in large quantities to print natural images as shown in FIGS.9A and 9B, together in one ink cartridge separately from the other colorinks preferably prevents the waste of the C, M, and Y inks when only theDY, LC, and LM inks are used up by printing a large number of naturalimages. The arrangement of keeping the K ink alone in one ink cartridgeseparately from the C, M, and Y inks also preferably prevents the wasteof the C, M, and Y inks when only the black ink is used up by printing alarge number of black and white images, such as documents.

[0221] As shown in the examples of FIGS. 8D through 8F, the DY ink maybe kept together with one or a plurality of other inks in one inkcartridge. This arrangement desirably saves the total space required forthe ink cartridges.

[0222] A special printer driver exclusively designed for the DY ink maybe attached to any one the ink cartridges including the DY ink as shownin FIGS. 8A through 8F. For example, when there are a plurality ofdifferent DY inks, the special printer driver attached to the inkcartridge is used corresponding to the DY ink.

[0223] As explicitly shown in FIG. 8A, the storage element 52 forstoring data, for example, with regard to the quantities of consumptionof the respective color inks is mounted on the side face of the inkcartridge 43. As described previously with FIG. 6, the color printer 20can read and write a variety of data from and into the storage element52. The following briefly describes the functions of the storage element52 mounted on the ink cartridge 43.

[0224]FIG. 10 is an enlarged view illustrating the storage element 52mounted on the side face of the ink cartridge 43. The storage element 52has a plurality of connection terminals 53. The ink cartridge 43 isattached to the carriage 40 of the color printer 20. The inner face ofthe carriage 40 that is in direct contact with the ink cartridge 43 hasa plurality of connectors (not shown) that are connected with theconnection terminals 53 of the storage element 52. When the inkcartridge 43 is attached to the carriage 40 of the color printer 20, theplurality of connection terminals 53 are electrically connected with theplurality of connectors on the carriage 40 to allow the datatransmission between the color printer 20 and the storage element 52.

[0225]FIG. 11 shows the data structure of the EEPROM incorporated in thestorage element 52. The numerals in the left column of FIG. 11 denotethe addresses in the storage element 52 seen from the color printer 20,and the right column of FIG. 11 shows the contents of the informationregistered at the respective addresses. The storage element 52 includesa first storage area 660 and a second storage area 650. The colorprinter 20 enables both the reading and writing operations of data fromand into the first storage area 660, whereas enabling only the readingoperation of data from the second storage area 650. Data on theremaining quantities of the respective color inks are stored in thefirst storage area 660. Other data that are not required updating norfrequently read, for example, the data on the year, month, and date ofmanufacture of the ink cartridge, are stored in the second storage area650. The first storage area 660 is allocated to a region of loweraddresses than those to the second storage area 650. The allocation ofthe first storage area 660, which data ate frequently read from andwritten in, to the region of the lower addresses ensures the quick datareading and writing operations by the sequential access. Thisarrangement enables application of an inexpensive EEPROM for theexpendable ink cartridges.

[0226] As shown in FIG. 11, the data on the remaining quantities of theC, M, Y, LC, LM, and DY inks are stored in the first storage area 660.The remaining quantities of the respective color inks are registered ina duplicated manner. The duplicate storage functions as the back-up whenthe data are destroyed, for example, by an accidental power breakdown inthe course of writing data. The remaining quantities of inks are storedwith regard to all the inks kept in the ink cartridge. In the case whereonly the DY ink is kept in the ink cartridge, for example, only theremaining quantity of the DY ink is-stored in the first storage area660.

[0227] The second storage area 650 stores the data on the time (year andmonth) of unsealing the ink cartridge, the version data of the inkcartridge, the data on the type of ink, for example, pigments or dyes,the data on the year, month, and date of manufacture of the inkcartridge, the data on the production line, the serial number data ofthe ink cartridge, and the data showing whether the ink cartridge is newor recycled.

[0228] The computer 80 reads the data from the storage element 52 atpredetermined timings, for example, at the time of power supply to thecolor printer 20, and writes the data on the remaining quantities of therespective inks into the storage element 52 at predetermined timings,for example, at the time of completion of the printing operation or atthe time of power cut to the color printer 20. This arrangement enablesthe printer driver 92 to accurately obtain the type of ink currentlyused and the remaining quantity of each ink. The color printer 20 of theembodiment thus enables appropriate printing operations and effectivelyprevents ink from being used up in the course of the printing operation.

[0229] A-3. Dark Yellow Ink

[0230]FIG. 12 shows an example of ink compositions used in the colorprinter 20 of the embodiment. Each color ink is a mixed solutionobtained by adding adequate quantities of each color dye and diethyleneglycol for the adjustment of the viscosity to an aqueous solution ofSurfinol. The dark yellow ink used in this embodiment is prepared byadding substantially equivalent quantities of Direct Blue 199, which isthe dye of the cyan ink, and Acid Red 289, which is the dye of themagenta ink, to Direct Yellow 86, which is the dye of the yellow ink.The composition of the dark yellow ink is, however, not restricted tothis example. The dark yellow ink may contain the varying ratio orquantities of Direct Blue 199 and Acid Red 289 or may be prepared byadding a small quantity of Food Black 2, which is the dye of the blackink, to Direct Yellow 86. The dark yellow ink may also have a lesscontent of Direct Yellow 86 by adding greater quantities of Direct Blue199 and Acid Red 289 or by adding a greater quantity of Food Black 2.The dye of the yellow component used for the dark yellow ink may beidentical with or different from the dye used for the yellow ink. Theyellow dyes, such as Direct Yellow 132 and Acid Yellow 23, may be usedin place of Direct Yellow 86, which is the yellow dye used for theyellow ink.

[0231] As clearly understood from the above explanation, the dark yellowink may have the following definition based on the ability ofreproducing colors in the color printer. The dark yellow ink has a lowerlightness than that of the yellow ink. Dots of the dark yellow ink cannot express achromatic gray color alone, but can represent theachromatic color in combination with dots of the cyan ink and dots ofthe magenta ink. In this embodiment, the viscosity of each color ink isadjusted to be approximately 3 mPa.s. The same control procedure canthus be applied for the piezoelectric elements PE allocated to any ink.

[0232]FIGS. 14A through 14E are graphs conceptually showing thevariations in reflectivity against the wavelength of light with regardto the color inks used in this embodiment. Referring to FIGS. 14Athrough 14C, the cyan (C) ink characteristically absorbs light in thewavelength region of 600 nm to 700 nm, the magenta (M) inkcharacteristically absorbs light in the wavelength region of 500 nm to600 nm, and the yellow (Y) ink characteristically absorbs light in thewavelength region of 400 nm to 500 nm.

[0233] The graphs of FIGS. 14D and 14E conceptually show the variationsin reflectivity against the wavelength of light with regard to differentdark yellow (DY) inks. DY1 ink shown in FIG. 14D corresponds to the DYink having the composition shown in FIG. 12, and DY2 ink shown in FIG.14E corresponds to the DY ink prepared by adding Food Black 2 to DirectYellow 86. Since the DY1 ink contains small quantities of the dyes ofthe cyan ink and the magenta ink in addition to the dye of the yellowink (see FIG. 12), the DY1 ink mainly absorbs the ray of the wavelengthregion characteristic of the yellow ink and also slightly absorbs therays of the wavelength regions characteristic of the cyan ink and themagenta ink. Varying the quantities of addition of Direct Blue 199 andAcid Red 289 changes the absorption the rays of the wavelength regionscharacteristics of the cyan ink and the magenta ink. Since the DY2 inkcontains a small quantity of the dye of the black ink in addition to thedye of the yellow ink, the DY2 ink mainly absorbs the ray of thewavelength region characteristics of the yellow ink and also increasesabsorption over the wavelength region of 500 nm to 700 nm. Varying thequantity of addition of Food Black 2 changes the absorption in thewavelength region of 500 nm to 700 nm. The graphs of FIG. 14D and 14Eexaggerate the difference in characteristics of light absorption betweenthe DY1 ink and the DY2 ink. The actual difference in characteristics oflight absorption between the DY1 ink and the DY2 ink is not so clear asthat illustrated here.

[0234] The comparison between the reflectivity of the DY1 ink or the DY2ink and the reflectivity of the Y ink shown in. FIG. 14C clearly showsthat the reflectivity of the DY1 ink or the DY2 ink is lowered in thewavelength region of visible rays. This means that both the DY1 ink andthe DY2 ink have lower lightness than that of the Y ink. The change incharacteristics of light absorption with a variation in quantities ofthe dyes added to the dye of the yellow component has certain effects asdiscussed later.

[0235]FIG. 13 is a graph showing the curves of lightness with regard tothe respective inks having the compositions shown in FIG. 12. The dotrecording ratio plotted as abscissa in the graph of FIG. 13 is an indexrepresenting the percent of dots formed per unit area. For example, thedot recording ratio of 100% represents the state in which dots areformed in all the pixels. The dot recording ratio of 50% represents thestate in which dots are formed in half the pixels. The dot recordingratio of 0% represents the state in which no dots are formed in anypixels. The dot recording ratio is explained in detail later. Thelightness plotted as ordinate in the graph of FIG. 13 represents thebrightness of the image relative to the background color of the printingpaper. The lightness of 100% represents the background color of theprinting paper. The brightness of the image decreases with a decrease inlightness. Any ink has the lightness of 100% at the dot recording ratioof 0%. The lightness decreases with an increase in dot recording ratio,that is, with formation of more dots. Comparison of the brightnessbetween the images at a fixed dot recording ratio shows the differencein lightness between the respective color inks.

[0236] The results of the measurement shown in FIG. 13 show that the DYink having the composition shown in FIG. 12 (corresponding to the DY1ink shown in FIG. 14D) is darker than the Y ink, the LC ink, and the LMink but brighter than the C ink, the M ink and the K ink.

[0237] The DY ink may have any composition as shown in the examples ofFIGS. 14D and 14E. FIG. 15 is a graph showing the observed curve ofreflectivity against the wavelength of light with regard to DY inkprepared according to a different principle from those of the DY1 inkand the DY2 ink (hereinafter referred to as the DY3 ink). For thepurpose of reference, the curve of reflectivity with regard to the DY1ink is also plotted by the dotted line. As shown in the graph of FIG.15, like the reflectivity of DY1 ink, the reflectivity of the DY3 inkhas a characteristic area of small reflectivity (that is, the areacharacteristically absorbing light) in the wavelength region of 400 nmto 500 nm. This is characteristic of the yellow ink. The reflectivity ofthe DY3 ink rises in a wavelength region of longer than about 650 nm. Itis known that the sensitivity of human eye to the color is abruptlylowered in the wavelength region of longer than about 650 nm. Althoughthe DY1 ink and the. DY3 ink have significantly different behaviors onreflectivity in the wavelength region of longer than 650 nm as shown inFIG. 15, they are recognized as substantially the same color by thevision of the human eye. This means that there is a significant degreeof freedom in setting of the light reflectivity in the wavelength regionof longer than 650 nm. It is not easy to specify the composition of therespective dyes or pigments in the ink for the ideal spectroscopiccharacteristics. The DY ink having the ideal hue is, however, easilyobtained by utilizing the degree of freedom in reflectivity in thewavelength region of longer than 650 nm. As is well known, thesensitivity of human eye to the color is lowered in the wavelengthregion of shorter than 400 nm, as well as in the wavelength region oflonger than 650 nm. The ink can thus be designed by utilizing the degreeof freedom in reflectivity in the short wavelength region.

[0238] The following describes, with FIG. 16, the phenomenon that theproperties of the DY ink can be regulated to some extent by utilizingthe degree of freedom in reflectivity in the wavelength region of longerthan 650 nm. FIG. 16 shows the observed colors expressed on the printingpaper under the condition of a gradual increase in recording density ofdots (dot recording ratio) formed with the DY ink on the printing paper.The abscissa represents the a* axis in the L*a*b* calorimetric system,and the ordinate represents the b* axis. The area of positive values (+)along the a* axis substantially corresponds to the red color, whereasthe area of negative values (−) along the a* axis substantiallycorresponds to the green color. The area of positive values (+) alongthe b* axis substantially corresponds to the yellow color, whereas thearea of negative values (−) along the b* axis substantially correspondsto the blue color. The position shown by ST in the graph of FIG. 16shows the coordinates representing the background color of the printingpaper.

[0239] In the case where dots are formed with the DY1 ink shown in FIG.15 on the printing paper, the color expressed on the printing paperfollows a locus shown by the dotted line with an increase in dotrecording ratio. Namely the hue becomes slightly greenish with anincrease in dot recording ratio. In the case where dots are formed withthe DY2 ink, on the other hand, the hue does not become greenish with anincrease in dot recording ratio. The minute characteristics of the inkas shown in FIG. 16 can be regulated by utilizing the wavelength regionof longer than 650 nm, where the sensitive of human eye to the color islowered to give a sufficient degree of freedom in design of the ink. Asdescribed later in detail, the use of the DY ink having the hue becominggreenish with an increase in dot recording ratio significantly improvesan image having the hue of green and low lightness. In a similar manner,the use of the DY ink having the hue becoming reddish with an increasein dot recording ratio significantly improves an image having the hue ofred and low lightness. The ink having the hue in a range of 10R to 10GYon a Munsell hue circle is applicable for the DY ink. In the example ofthe DY3 ink shown in FIG. 15, the reflectivity of light is increased inthe wavelength region of longer than 650 nm by utilizing the degree offreedom in design of the ink in this wavelength region. The ink mayalternatively be designed to lower the reflectivity of light in thiswavelength region.

[0240]FIG. 17 shows the structure of an ink supplier 55 for feeding asupply of ink to an ink cartridge. The ink supplier 55 includes a sealedvessel 56, in which ink is sealed, a filler inlet 57, through which asupply of ink is fed, and a piston 58 to press the sealed ink out. Thedark ink discussed above is sealed in the sealed vessel 56 to be notexposed to the atmosphere. This protects the ink in the ink supplier 55from a change in properties. When a supply of ink is fed to the inkcartridge, a cap 54 mounted on an end of the filler inlet 57 of the inksupplier 55 is removed, and the filler inlet 57 is stuck to an inksupply inlet (not shown) formed in the bottom face of the ink cartridge.The piston 58 is then pressed down to slowly press the ink out of thesealed vessel 56, so as to feed a supply of ink to the ink cartridge.

[0241] B. Image Processing

[0242] The color printer 20 forms dots of the respective color inksincluding the DY ink discussed above, so as to print a color image. Inorder to enable the color printer 20 to create dots of the respectivecolor inks, the computer 80 should carry out predetermined imageprocessing with regard to image data ORG representing a color originalimage and output the processed image data FNL to the color printer 20.The image processing is executed by the printer driver 92 of thecomputer 80. FIG. 18 is a flowchart showing an image processing routineexecuted by the printer driver 92.

[0243] When the program enters the image processing routine of FIG. 18,the CPU 81 in the computer 80 first receives image data to be processedat step S100. As described previously with FIG. 2, the image data aregenerated by the application program 91 and transmitted to the printerdriver 92. In the application program 91, the color image data areexpressed as a combination of three color images, red (R), green (G),and blue (B). The image of each color is expressed as a set of pixelsindividually having tone values. In the case of 8-bit image data, eachpixel may take one of 256 tone values in a range of 0 to 255.

[0244] B-1. Process of Converting Resolution

[0245] When receiving the image data output from the application program91, the CPU 81 carries out a process of converting resolution at stepS102. As mentioned above, the input image is expressed as a set ofpixels. The length on a printing medium corresponding to one pixeldepends upon the size of an image to be processed on the printingmedium. The number of dots printable per unit length by the printer(hereinafter referred .to as the printer resolution) has been set foreach model of the printer. For convenience of the image processing, itis required to make the resolution of the image coincident with theprinter resolution. In the case where the resolution of the image islower than the printer resolution, linear interpolation is performed togenerate a new piece of image data between two adjacent pieces ofexisting data. In the case where the resolution of the image is higherthan the printer resolution, on the contrary, the resolution is loweredby skipping some pieces of image data at a preset rate. The process ofstep S102 makes the resolution of the image coincident with the printerresolution in this manner.

[0246] B-2. Color Conversion Process

[0247] After completion of the resolution conversion process, the CPU 81carries out a color conversion process at step S104. As describedpreviously, the application program 91 expresses a color image as toneimage data of three colors, red (R), green (G), and blue (B). The colorprinter 20, on the other hand, expresses a color image, in principle, bysubtractive mixture of three color stimuli, cyan (C), magenta (M), andyellow (Y). In order to print a color image, it is accordingly requiredto convert the expression of a color image with the three colors R, G,and B to the expression of a color image with the three colors C, M, andY. The process of step S104 carries out such color conversion. Theactual process of this embodiment carries out the color conversion notto the three basic colors C, M, and Y but to the total of seven colorsincluding K, LC, LM, DY. For the clarity of explanation, however, it isassumed that the process carries out the color conversion to the threebasic colors C, M, and Y. The color conversion process changes the toneimage data of R, G, and B respectively having the 256 tone values totone image data of C, M, and Y respectively having the 256 tone values.

[0248] In the actual procedure, the CPU 81 refers to a conversion tableas shown in FIG. 19, so as to convert the R, G, and B tone values intothe C, M, and Y tone values. As shown in FIG. 19, the conversion tableis a three-dimensional mathematical table (color solid) having the tonevalues of R, G, and B as axes. In this embodiment, each axis takes thevalues in the range of 0 to 255. A space defined by the mutuallyperpendicular R, G, and B axis is referred to as the color space. Theconversion table divides the color solid into a number of small cubes.Each cube has vertexes, at each of which a corresponding set of the C,M, and Y tone values is registered.

[0249] The color conversion is carried out in the following manner byreferring to the conversion table. For example, it is assumed that acolor defined by RA, GA, and BA as the tone values of R, G, and B is tobe expressed by the tone values of C, M, and Y. The process finds asmall cube (dV) including a point A having the coordinates (RA, GA, BA)in the color space. The process then carries out interpolation with setsof the C, M, and Y tone values registered at the respective vertexes ofthe cube (dV), so as to calculate the C, M, and Y tone values of thepoint A.

[0250] In this manner, the conversion table allocates a set of the C, M,and Y tone values to each coordinate included in the color solid of R,G, and B tone values. When tone values of the K (black), LC (lightcyan), LM (light magenta), and DY (dark yellow) are registered, inaddition to the tone values of the C, M, and Y, in the conversion table,a set of the C, M, Y, K, LC, LM, and DY tone values is allocated to eachcoordinate included in the color solid of R, G, and B tone values. Inaccordance with another possible application, intermediate sets of C, M,and Y tone values, sets of C, M, Y, and K values, or sets of C, M, Y, K,LC, and LM tone values may be stored in the conversion table. Theprocess calculates the final tone values of C, M, Y, K, LC, LM, and DYfrom the intermediate values stored in the conversion table.

[0251]FIGS. 20A and 20B conceptually show a method of calculating tonevalues of seven colors C, M, Y, K, LC, LM, and DY from the tone valuesof six colors C, M, Y, K, LC, and LM in a shadow area (area having lowlightness). FIG. 20A shows an example in the shadow area of dark red.The tone values of LC and LM are extremely small, while the tone valuesof C, M, and Y are large in the shadow area as shown in FIG. 20A. Thetone value of each color corresponds to the density of dots formed withthe color ink on the printing medium.

[0252]FIG. 20B shows a case in which half the tone value of Y isreplaced with the tone value of DY. As explained previously with FIG. 2,the DY ink has certain contents of the dyes of the cyan ink and themagenta ink. The tone values of C and M are accordingly reduced by theproducts of the DY tone value and the rates of content of the respectivedyes. As shown in FIG. 20B, the reduction results in producing a marginfor the restriction of ink duty.

[0253] In order to increase the darkness of the dark red from the stateshown in FIG. 20A, it is required to decrease the tone values of C, M,and Y and increase the tone value of K (that is, create K dots). Asdescribed previously, however, creation of K dots results in the poorgranularity unless the K dots are formed in very dark red. When there isa certain margin for the restriction of ink duty as shown in FIG. 20B,the dark red can be further darkened by increasing the tone value of LCor C. This prevents the poor granularity due to creation of K dots. Themargin for the restriction of ink duty is enhanced by increasing therate of replacement of the Y tone value with the DY tone value or byincreasing the contents of the dyes of the cyan ink and the magenta inkincluded in the DY ink, as described later.

[0254] In most cases, the color correction process is carried outsimultaneously with the color conversion process. The color correctionprocess corrects the tone values of R, G, and B, in order to eliminatethe effects of different sensitivity characteristics of image scannersthat read color images. Alternatively the color correction processcorrects the tone values of C, M, and Y, in order to eliminate thedifference in color reproduction properties between the printingapparatuses. The color correction enables accurate colors to bereproduced irrespective of the difference between the image scanners orthe printing apparatuses.

[0255] B-3. Process of Converting Number of Tones

[0256] After the completion of the color conversion process, the CPU 81carries out a process of converting the number of tones at step S106.The image data after the color conversion represents an image of 256tones with regard to the seven colors C, M, Y, K, LC, LM, and DY. Theprinter, on the other hand, creates dots on the printing paper toreproduce an image, and generally has only two levels, that is, thedot-on state and the dot-off state. There are variable dot printers andother multi-level printers that can print multi-level dots includingintermediate states, for example, by varying the size of dots to becreated. These printers, however, still have a relatively small numberof expressible tones. It is thus required to convert the image having256 tones into an image having an extremely small number of tonesexpressible by the printer. This is the process of converting the numberof tones. FIGS. 21A and 21B show a process of binarization to convertthe number of tones. FIG. 21A shows image data after the colorconversion but before the binarization, and FIG. 21B shows image dataafter the binarization. The image data before the binarization have anyone of 256 tones in each pixel. The image data after the binarizationhave either one of two values in each pixel, that is, the dot on level(the value ‘1’) and the dot-off level (the value ‘0’). In order to showthe distribution of dots clearly, in the image data of FIG. 21B, pixelshaving the value ‘1’ are hatched and pixels having the value ‘0’ areopen.

[0257] The structure of this embodiment determines the dot on-offconditions with regard to the seven colors C, M, Y, K, LC, LM, and DY.There are a variety of methods applicable for the determination, all ofwhich naturally have some advantages and disadvantages. The colorprinter 20 of the embodiment causes the user to select an appropriatemethod for the determination. There are typically two methods, the errordiffusion method and the systematic dither method. The error diffusionmethod ensures the high picture quality, whereas the systematic dithermethod enables the high-speed processing. The following brieflydescribes the outlines of the error diffusion method and the systematicdither method.

[0258] B-4. Binarization by Error Diffusion Method

[0259]FIG. 22 is a flowchart showing a binarization process by the errordiffusion method. The technique of the embodiment carries out thebinarization process individually with regard to the respective colorsC, M, Y, K, LC, LM, and DY after the color conversion. The followingdescription does not specify the color, for the clarity of explanation.When the program enters the binarization process, the CPU 81 reads imagedata Cd at step S200. The image data Cd have 256 tones with regard toeach color after the color conversion. The CPU 81 generatescorrection-data Cdx from the input image data Cd at step S202. The errordiffusion method distributes an error of binarization generated withregard to each processed pixel to a plurality of unprocessed pixels inthe vicinity of the processed pixel with certain weights. The process ofstep S202 adds a sum of error portions distributed from the surroundingprocessed pixels to a pixel of interest, which is currently beingprocessed, to calculate the correction data Cdx. FIG. 23 shows theweights added to the surrounding pixels, to which an error of a pixel ofinterest PP is distributed. The error of binarization generated in thepixel of interest PP is distributed to several adjoining pixels in thescanning direction of the carriage, as well as to several adjoiningpixels in the feeding direction of the printing paper P withpredetermined weights, ¼, {fraction (1/8)}, and {fraction (1/16)}. Theerror diffusion process is described later more in detail. Thecorrection data Cdx thus generated is compared with a predeterminedthreshold value th set for each color at step S204. In the case wherethe correction data Cdx is not smaller than the threshold value th, avalue ‘1’ representing creation of a dot is set to a resulting value Cdrshowing the result of the binarization at step S206. In the case wherethe correction data Cdx is smaller than the threshold value th, on theother hand, a value ‘0’ representing creation of no dot is set to theresulting value Cdr at step S208. The predetermined threshold value this a reference value used to determine whether or not a dot is to becreated in each pixel.

[0260] The CPU 81 then calculates an error of binarization in the pixelof interest and diffuses the calculated error to the peripheral pixelsin the vicinity of the pixel of interest at step S210. The error isequal to a difference by subtracting the result of the tone numberconversion from the tone value of the original image data. For example,it is assumed that there is a pixel having the tone value ‘64’ in theoriginal image data. When a dot is created in the pixel, the convertedresult corresponding to a tone value ‘255’ is expressed in the pixel. Inthis case, there is an error of 64−256=−191. When no dot is created inthe pixel, on the contrary, there is an error of 64−0=64.

[0261] The error thus calculated is diffused into the peripheral pixelswith the certain weights shown in FIG. 23. For example, when the targetof pixel PP has the calculated error corresponding to the tone value‘64’, an error portion corresponding to a tone value ‘16’, which is ¼ ofthe error, is diffused to an adjoining pixel P1. The total of suchdiffused errors is reflected on the image data Cd, so as to generate thecorrection data Cdx at step S202 described above. The series of theprocessing is repeated with regard to all the pixels at step S212. Theimage data representing the dot on-off conditions as shown in FIG. 21Bare eventually obtained.

[0262] The method of performing the color conversion to generate thetone image data of seven colors C, M, Y, K, LC, LM, and DY and carryingout the binarization individually for the respective colors simplifiesthe contents of the processing with regard to each color and thusenables the quick processing. The independent and simplified processingwith regard to each color enables parallel data conversion using anexclusive image processing apparatus. This arrangement ensures the quickbinarization even by the error diffusion method.

[0263] In the case of the binarization by the error diffusion method,another possible procedure applicable to the color conversion process(step S104 in the flowchart of FIG. 18) generates image data of the fourbasic colors C, M, Y, and K, and determines the dot on-off conditions ofthe C and LC dots based on the tone data of C, the dot on-off conditionsof the M and LM dots based on the tone data of M, and the dot on-offconditions of Y and DY dots based on the tone data of Y. This methodsimplifies and speeds up the color conversion process.

[0264] B-5. Binarization by Systematic Dither Method

[0265] The principle of binarization by the systematic dither method isdescribed with FIG. 24. In this example, it is assumed that the imagedata Cd may take the value in the range of 0 to 255, and a dither matrixhas values in the range of 0 to 254. For simplicity of explanation, theexample of FIG. 24 shows only part of the image data corresponding to4×4 pixels. As shown in FIG. 24, the tone values of the image data Cd inthe respective pixels are compared with the corresponding thresholdvalues included in the dither matrix. In the case where the value of theimage data Cd is greater than the corresponding threshold value in thedither matrix, the dot is to be created. In the case where the value ofthe image data Cd is not greater than the corresponding threshold value,on the other hand, the dot is not to be created. The pixels hatched inFIG. 24 represent pixels in which the dot is to be created.

[0266] As described above, the binarization by the systematic dithermethod compares the tone values of the image data in the respectivepixels with the corresponding threshold values included in the dithermatrix, and determines the dot on-off conditions in all the pixels withregard to the seven colors C, M, Y, K, LC, LM, and DY based on theresults of the comparison.

[0267] Like in the case of the binarization by the error diffusionmethod described previously, in the case of the binarization by thesystematic dither method, another possible procedure applicable to thecolor conversion process (step S104 in the flowchart of FIG. 18)generates image data of the four basic colors C, M, Y, and K, anddetermines the dot on-off conditions of the C and LC dots based on thetone data of C, the dot on-off conditions of the M and LM dots based onthe tone data of M, and the dot on-off conditions of Y and DY dots basedon the tone data of Y. The color conversion process of this procedurerequires the image data generated only with regard to the four colors.This arrangement simplifies the color conversion process. Thisarrangement also prevents dots of the same color system, for example, aC dot and an LC dot, from being formed in an overlapping manner in onepixel, thereby improving the picture quality.

[0268] B-6. Interlace Process

[0269] Referring back to the flowchart of FIG. 18, after the completionof the process of converting the number of tones, the CPU 81 starts aninterlace process at step S108. The interlace process reorders the imagedata, which have been converted to the dot on-off conditions by theprocess of converting the number of tones, in a sequent to betransferred to the color printer 20. As discussed above, the colorprinter 20 drives the print head 41 to form rows of dots (raster lines)on the printing paper P while repeating the main scan and the sub-scanof the carriage 40. As described previously with FIG. 4, each of the inkejection heads 44 through 50 has the plurality of nozzles Nz, so that aplurality of raster lines are formed by each pass of the main scan. Eachpair of adjoining raster lines formed by the same pass are apart fromeach other by the nozzle pitch k. Raster lines aligned at the intervalsof each pixel are formed according to the following control procedure.The control procedure first forms a plurality of raster lines at theintervals of the nozzle pitch k, slightly shifts the position of eachink ejection head, and forms new raster lines between the existingraster lines. In order to improve the picture quality of the resultingprinted image, the control procedure may cause each raster line to beformed by plural passes of the main scan. In order to shorten theprinting time, the control procedure may cause dots to be formed by bothforward passes and backward passes of the main scan.

[0270] After completion of the interlace process, the image data areoutput as the printable image data FNL to the color printer 20 at stepS110.

[0271] C. Results of Simulations

[0272] In order to confirm the effects of the DY ink on the improvementin picture quality, the simulative computation discussed below wascarried out. The following conditions were set for the simulativecomputation:

[0273] Condition 1: The color ‘red’ is expressed by forming both M dotsand Y dots at a dot recording ratio of 100%;

[0274] Condition 2: The color ‘black’ is expressed by forming K dots ata dot recording ratio of 100%;

[0275] Condition 3: K dots are equivalently replaceable with acombination of C Dots, M dots, and Y dots at the same density as that ofthe K dots;

[0276] Condition 4: LC dots are equivalently replaceable with C dots ata ¼ dot recording ratio;

[0277] Condition 5: LM dots are equivalently replaceable with M dots ata ¼ dot recording ratio; and

[0278] Condition 6: DY dots are equivalently replaceable with acombination of LC dots, LM dots, and Y dots at the same density as thatof the DY dots.

[0279] The actual printing operation is performed under more complicatedconditions. For example, the rate of replacement of each ink (that is,the rate of each color ink that does not change the output color byreplacement) varies in a very complicated manner according to the actualprinting conditions, and rarely gives a fixed value as shown by theabove conditions. The results of the simulations discussed below do notstrictly represent the actual printing results. The qualitative effectsof the DY ink on the improvement in picture quality by the simulativecomputation are, however, sufficiently applicable to the actual printingresults.

[0280] C-1. Gradation Pattern from Red to Black

[0281]FIGS. 25A, 25B, and 25C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern gradually becoming dark from red to blackwith the color printer 20 of the embodiment. According to the aboveconditions, the gradation pattern from red to black is a pattern havingthe linearly increasing dot recording ratio of C dots from 0% to 100%while keeping a dot recording ratio of 100% with regard to both the Mdots and the Y dots.

[0282] On the abscissa of each graph, the value of 0% represents thepure color ‘red’ and the value of 100% represents the pure color‘black’. The color ‘red’ expressed on the printing paper is graduallydarkened with an increase in value on the abscissa. FIG. 25A shows theresults of the simulation with the dots of the DY ink in the case ofusing a sheet of printing paper having a restriction of ink duty equalto 220%.

[0283] As shown in FIG. 25A, at the value of 0% on the abscissa (thepure color ‘red’), only the M dots and the Y dots are formed at the dotrecording ratio of 100% on the printing paper. The lightness of thecolor is lowered (that is, darkened) with an increase in dot recordingratio of the LC dots while keeping the dot recording ratios of both theM dots and the Y dots at 100%. When the dot recording ratio of the LCdots reaches 20% (approximately 5% on the abscissa), the total recordingratio of the Y, M, and LC dots becomes equal to 220%. The restriction ofink duty set for the printing paper does not allow creation of dots atthe greater density. Formation of the DY dots is thus commenced at thevalue of about 5% on the abscissa, while the dot recording ratio of theY dots is gradually decreased. The DY dots formed in the hue of red arenot so conspicuous, because of the following reason. According to theabove condition 6, formation of the DY dots is equivalent to formationof the Y dots, the LM dots, and the LC dots at the same quantity as thatof the DY dots. The Y dots or the LM dots formed in an image where boththe Y dots and M dots have been formed at the dot recording ratio of100% are inconspicuous against the background. The conspicuousness ofthe DY dots formed in the hue of red is as low as that of the LC dots,and the DY dots are thus significantly inconspicuous.

[0284] It can be assumed that the DY ink includes the LC ink and the LMink in addition to the Y ink (condition 6 given above). Formation of theDY dots accordingly decreases the dot recording ratios of both the LCdots and the M dots. The decrease in dot recording ratios of the LC dotsand the M dots gives a certain margin for the restriction of ink duty,and thus allows a further increase in dot recording ratio of the LCdots. After the sum of the dot recording ratios of the M, Y, and LC dotsreaches the restriction of ink duty, the replacement of the Y dots withthe DY dots enables the lightness of the color ‘red’ expressed on theprinting paper to be lowered (that is, the value on the abscissa to beincreased). In this stage, no use of the conspicuous C dots desirablyprevents the granularity from being worsened.

[0285] After the perfect replacement of all the Y dots with the DY dots,no further increase in formation of the DY dots is allowed. The value onthe abscissa is accordingly increased by gradually replacing the LC dotswith the C dots having the higher density. Formation of the C dots iscommenced at the value of about 40% on the abscissa as shown in thegraph of FIG. 25A. The C dots have a relatively low lightness and arerather conspicuous in the color of bright red to worsen the granularity.As in the case of FIG. 25A, however, the C dots are not so conspicuousin the color of dark red, which is expressed by the value of bout 40% onthe abscissa, thereby not worsening the granularity.

[0286] When the sum of the dot recording ratios of the C, M, and DY dotsreaches the restriction of ink duty, no further increase in formation ofdots is allowed. The dot recording ratios of the respective C, M, and DYdots are thus decreased, while formation of the K dots is commenced. Asdescribed previously, the K dots have an extremely low lightness (thatis, the K dots are very dark) and are rather conspicuous tosignificantly worsen the granularity, unless they are formed in thesufficiently dark background. As shown in FIG. 25A, however, formationof the K dots is commenced at the value of about 70% on the abscissa.The color ‘red’ expressed on the printing paper thus already has asignificantly low lightness, so that the K dots are not conspicuous tolower the picture quality. At the final stage, only the K dots areformed at the dot recording ratio of 100%. The gradation pattern printedon the printing paper thus naturally and gradually changes the colorfrom red, where only the M dots and the Y dots are formed at therecording ratio of 100%, to black, where only the K dots are formed atthe recording ratio of 100%. Formation of the C dots is commenced at thevalue of about 40% on the abscissa, and formation of the K dots iscommenced at the value of about 70% on the abscissa. These dots areaccordingly not conspicuous to lower the picture quality.

[0287]FIG. 25B shows the results of the simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black without the DY dots onthe sheet of printing paper having the restriction of ink duty equal to220%. The pure color ‘red’ (the value of 0% on the abscissa) isgradually darkened with an increase in dot recording ratio of the LCdots. Due to the restriction of ink duty, formation of the C dots shouldbe commenced when the dot recording ratio of the LC dots reaches 20%. Inthis case, formation of the C dots is required at the value of about 5%on the abscissa, where the color of still bright red is expressed on theprinting paper. While the LC dots formed in the color of bright red arenot so conspicuous, the C dots, which have a higher density than that ofthe LC dots, formed in the color of bright red as in the case of FIG.25B are rather conspicuous and worsen the granularity.

[0288] After the perfect replacement of all the LC dots with the C dots,no further increase in formation of dots is allowed due to therestriction of ink duty. Formation of the K dots is accordinglycommenced, while the dot recording ratios of the M dots and the Y dotsare gradually decreased. This state is at the value of about 25% on theabscissa in the graph of FIG. 25B. Since the K dots have an extremelylow lightness (that is, the K dots are very dark), formation of the Kdots at the value of about 25% on the abscissa significantly worsens thegranularity.

[0289] As described above, when the gradation pattern from red to blackis printed without using the DY ink on the printing paper having therestriction of ink duty equal to 220%, the C dots are conspicuous in thecolor of still bright red and the K dots are conspicuous in the color ofrelatively dark red. This gives an image of the poor granularity. Inother words; the use of the DY ink improves the granularity. If the DYdots themselves are rather conspicuous, the use of the DY ink ismeaningless even though the DY ink prevents the granularity from beingworsened due to the C dots or the K dots. The components of the Y inkand the LM ink included in the DY ink are not conspicuous against thebackground ‘red’ color. This means that only the component of the LC inkincluded in the DY ink has a possibility of conspicuousness. Theconspicuousness of the DY dots formed in the red background is thussubstantially equivalent to that of the LC dots. The use of the DY inkaccordingly gives an image of extremely favorable granularity withoutany significant conspicuousness of dots.

[0290]FIG. 25C shows the results of the simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from red to black without the DY dots onanother sheet of printing paper having a restriction of ink duty equalto 260%. The pure color ‘red’ (the value of 0% on the abscissa) isgradually darkened with an increase in dot recording ratio of the LCdots. Due to the restriction of ink duty, replacement of the LC dotswith the C dots should be commenced to further darken the color of redwhen the dot recording ratio of the LC dots reaches 60% (the value of15% on the abscissa) When the dot recording ratio of the C dots reaches60% (the value of 65% on the abscissa), no further formation of the Cdots is allowed. Formation of the K dots is thus commenced, while thedot recording ratios of the C, M, and Y dots are gradually decreased. Atthe final stage, only the K dots are formed at the dot recording ratioof 100% (pure ‘black’ color). According to the comparison between thegraphs of FIGS. 25A and 25C, both the timing of commencing the formationof the C dots and the timing of commencing the formation of the K dotsare earlier in the case of FIG. 25C than in the case of FIG. 25A. Namelythe dots are more conspicuous to worsen the granularity in the case ofFIG. 25C, compared with the case of FIG. 25A. Based on the simulationconditions given previously, the improvement in picture quality by usingthe DY ink is greater than the improvement in picture quality bychanging the printing paper having the restriction of ink duty equal to220% to the printing paper having the restriction of ink duty equal to260%.

[0291] The above results of the simulations suggest the usage of the DYink. In the case of printing a gradation pattern from red to black, theformation of dots with the DY ink starts prior to the formation of dotswith the C ink. The DY ink has a hue closest to that of the Y ink amongthe three basic color inks, C, M, and Y. The dots of the M ink and thedots of the Y ink have been created in advance to express the hue ofred. The formation of dots with the DY ink is thus not commenced earlierthan the formation of dots with the M ink and the Y ink.

[0292] There is another suggestion with regard to the usage of the DYink. In the case of printing a gradation pattern from red to black,formation of the dots with the DY ink starts after the formation of dotswith the LC ink. The DY ink has a hue closest to that of the Y ink amongthe three basic color inks, C, M, and Y. It can thus be thought that thedots of the DY ink are created together with the dots of the LC ink.

[0293] In the prior art color printer using the six color inks, C, M, Y,K, LC, and LM, the quantities of consumption of the Y, LC, and LM inksare greater than the quantities of consumption of the C and M inks. Asdescribed previously, the C, M, Y, LC, and LM inks are often kept in oneink cartridge 43. According to images to be printed, the Y, LC, and Minks are used up to require a replacement of the ink cartridge 43 thatstill has the remains of the C and M inks. The color printer 20 of theembodiment uses the DY ink in place of the Y ink in some occasions andthereby decreases the quantity of consumption of the Y ink. Since the DYink contains the dyes of cyan and magenta, the use of the DY ink alsodecreases the quantities of consumption of the LC ink and the LM ink.The use of the DY ink thus enables all the other color inks to beconsumed in a relatively equal manner and desirably reduces thefrequency of replacement of the ink cartridge. The DY ink may be kepttogether with the LC ink and the LM ink in the same ink cartridge. Thisenables replacement of only the ink cartridge including the LC, LM, andDY inks having the greater quantities of consumption.

[0294] The above description regards the gradation pattern from red toblack. The gradation pattern from red to black is only an example ofgradation patterns starting from the condition that dots of only twocolor inks (in this example, the Y dots and the M dots) have alreadybeen formed. Similar effects are thus naturally exerted in the case ofprinting a gradation pattern from green to black with replacement of theM dots with the C dots and the LM dots with the LC dots. The effects ofvarying the quantities of the cyan dye and the magenta dye added to theDY ink will be described later.

[0295] C-2. Gradation Pattern from Magenta to Black

[0296]FIGS. 26A, 26B, and 26C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black with the colorprinter 20 of the embodiment. The conditions set for the simulativecomputation are identical with the conditions used for the simulation ofthe gradation pattern from red to black. FIG. 26A shows the results ofthe simulative computation with the DY dots in the case of the printingpaper having the restriction of ink duty equal to 220%. FIG. 26B showsthe results of the simulative computation without the DY dots in thecase of the printing paper having the restriction of ink duty equal to220%. FIG. 26C shows the results of the simulative computation withoutthe DY dots in the case of the printing paper having the restriction ofink duty equal to 260%.

[0297] As shown in FIG. 26A, in the gradation pattern from magenta toblack, the dot recording ratios of the LC dots and the Y dots aregradually increased from the initial state (the value of 0% on theabscissa) in which the M dots have a dot recording ratio of 100%.According to the condition 4 mentioned previously, the dots of the LCink are equivalent to ¼ dots of the C ink. The rate of increase in dotrecording ratio of the LC dots is thus four times the rate of increasein dot recording ratio of the Y dots. When the dot recording ratios ofthe LC dots and the Y dots increase and the sum of the dot recordingratios of the M dots, the Y dots, and the LC dots reach the restrictionof ink duty, replacement of the Y dots with the DY dots is commenced.After the perfect replacement of all the Y dots with the DY dots,replacement of the LC dots with the C dots is commenced. According tothe results of the simulation shown in FIG. 26A, the formation of the Cdots starts at the value of about 35% on the abscissa. As describedpreviously, the DY ink contains the components of the LM ink and the LCink, formation of the DY dots is equivalent to formation of the samenumber of the LM dots and the LC dots (see the condition 6 mentionedabove). The increase in dot recording ratio of the DY dots accordinglydecreases the dot recording ratio of the M dots and reduces the rate ofincrease in formation of the C dots.

[0298] When the sum of the dot recording ratios of the C, M, and DY dotsreaches the restriction of ink duty, formation of the K dots iscommenced. According to the results of the simulation shown in FIG. 26A,the formation of the K dots starts at the value of about 80% on theabscissa. The increase in dot recording ratio of the K dots decreasesthe dot recording ratios of the C, M, and DY dots. At the final stage,only the K dots are formed at the dot recording ratio of 100% (pure‘black’ color). The resulting printed image on the printing paper is agradation pattern having the hues gently changing from magenta to black.

[0299] While FIG. 26A shows the results of the simulation with the DYdots, FIG. 26B shows the results of the simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black without the DY dotson the printing paper having the restriction of ink duty equal to 220%.Compared with the case with the DY dots shown in FIG. 26A, in the casewithout the DY dots shown in FIG. 26B, the formation of the C dots iscommenced at the slightly earlier timing and the formation of the K dotsis commenced at the significantly earlier timing. Starting the formationof the K dots at the value of about 60% on the abscissa like the resultsof the simulation shown in FIG. 26B drastically worsens the granularityof the resulting printed image. In other words, the use of the DY dotssignificantly improves the granularity of the resulting printed image.The improvement in granularity is attained by the fact that the DY inkcontains the cyan dye and the magenta dye. Formation of the DY dots isequivalent to formation of certain quantities of the C dots and the Mdots that correspond to the contents of the dyes. Replacement of the Ydots with the DY dots in a shadow area (for example, in the area havingthe value of about 75% on the abscissa) decreases the dot recordingratios of the M dots and the C dots. This ensures a certain margin forthe restriction of ink duty and thereby delays the timing of startingthe formation of the K dots.

[0300] As described above, the use of the DY dots significantly delaysthe timing of starting the formation of the K dots and slightly delaysthe timing of starting the formation of the C dots. This results in asignificant improvement in granularity. If the DY dots that startformation at a relatively early timing are conspicuous, the granularityof the resulting printed image is not actually improved. Theconspicuousness of the DY dots is thus a key factor. As describedpreviously, the DY ink includes the components of the LM ink, the LCink, and the Y ink (see the condition 6 mentioned above). When the dotsof the DY ink are formed in the magenta background, the component of theLM ink included in the DY ink is inconspicuous against the background.The dots of the other ink components, that is, the LC dots and the Ydots, are not so conspicuous in the magenta background. Formation of theDY dots is substantially equivalent to formation of the LC dots and theY dots in an overlapping manner. The dots of both the LC ink and the Yink are not so conspicuous as the dots of the C ink and the K ink.Formation of the DY dots in the magenta background even at a relativelyearly timing thus does not significantly worsen the granularity. In thecase of printing a gradation pattern from magenta to black, the use ofthe DY dots desirably delays the timings of starting the formation ofthe C dots and the K dots and thus significantly improves thegranularity of the resulting printed image.

[0301]FIG. 26C shows the results of the simulative computation of thedot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from magenta to black without the DY dotson the printing paper having the restriction of ink duty equal to 260%.The results of the simulative computation shown in FIG. 26C are comparedwith those shown in FIG. 26A. The timings of starting the formation ofthe C dots and the K dots in the case of FIG. 26C are almost the same asthose in the case of FIG. 26A. When a gradation pattern from magenta toblack is printed, substantially similar effects of improvement inpicture quality are attained in the case of printing with the DY dots onthe printing paper having the restriction of ink duty equal to 220% andin the case of printing without the DY dots on the printing paper havingthe restriction of ink duty equal to 260%.

[0302] As shown in the results of the simulations in FIGS. 26A, 26B, and26C, in the case of printing a gradation pattern from magenta to black,the use of the DY dots effectively prevents the granularity from beingworsened and thereby improves the picture quality of the resultingprinted image. Another effect of using the DY ink is reducing thequantities of consumption of the Y ink, the LC ink, and the LM ink.

[0303] The above results of the simulations suggest the usage of the DYink. In the case of printing a gradation pattern from magenta to black,the formation of dots with the DY ink starts prior to the formation ofdots with the C ink and after the formation of dots with the Y ink. TheDY ink has a hue closest to that of the Y ink among the three basiccolor inks, C, M, and Y. The dots of the M ink have been created inadvance to express the hue of magenta.

[0304] There is another suggestion with regard to the usage of the DYink. In the case of printing a gradation pattern from magenta to black,formation of the dots with the DY ink starts after the formation of dotswith the LC ink. The DY ink has a hue closest to that of the Y ink amongthe three basic color inks, C, M, and Y. It can thus be thought that thedots of the DY ink are created together with the dots of the LC ink.

[0305] The above description regards the gradation pattern from magentato black as an example of gradation patterns starting from the conditionthat dots of only one color ink have already been formed. Similareffects are thus naturally exerted in the case of printing a gradationpattern from cyan or yellow to black with replacement of the M dots withthe C dots or the Y dots.

[0306] C-3. Gradation Pattern from White to Black

[0307]FIGS. 27A, 27B, and 27C show results of simulative computation ofthe dot recording ratio with regard to each color ink in the case ofprinting a gradation pattern from white to black with the color printer20 of the embodiment. The conditions set for the simulative computationare identical with the conditions used for the simulation of thegradation pattern from red to black. FIG. 27A shows the results of thesimulative computation with the DY dots in the case of the printingpaper having the restriction of ink duty equal to 220%. FIG. 27B showsthe results of the simulative computation without the DY dots in thecase of the printing paper having the restriction of ink duty equal to220%. FIG. 27C shows the results of the simulative computation withoutthe DY dots in the case of the printing paper having the restriction ofink duty equal to 260%.

[0308] As shown in FIG. 27A, in the case of printing a gradation patternfrom white to black, formation of the LC dots, the LM dots, and the Ydots gradually increases from the initial state in which no dots havebeen formed. When the dot recording ratios of the LC dots and the LMdots approach to 100%, replacement of the LC dots and the LM dotsrespectively with the C dots and the M dots is commenced. The DY inkcontains the components of the LC ink and the LM ink (see the condition6 given previously). Replacement of the Y dots with the DY dots beforethe dot recording ratios of the LC dots and the LM dots reach 100% thuseffectively delays the timings of starting the formation of the C dotsand the M dots. The delay of the timings of starting the formation ofthe C dots and the M dots desirably makes the dots more inconspicuousand thereby prevents the granularity from being worsened in theresulting printed image.

[0309] With an increase in dot recording ratios of the C, M, and DYdots, the lightness of the color expressed on the printing paper isgradually lowered to darker gray. When the sum of the dot recordingratios of the C, M, and DY inks reaches the restriction of ink duty,formation of the K dots is commenced and the dot recording ratios of theC, M, and DY dots are gradually decreased. At the final stage, only theK dots are formed at a dot recording ratio of 100%. The resultingprinted image on the printing medium is a gradation pattern having thecolor gently changing from white to black.

[0310] The results of the simulation in the case with the DY dots shownin FIG. 27A are compared with the results of the simulation in the casewithout the DY dots shown in FIG. 27B. The formation of the DY dotsdesirably delays the timing of starting the formation of the K dots.According to the condition 6 mentioned previously, the DY ink containsthe components of the LC ink, the LM ink, and the Y ink. Replacement ofthe Y dots with the DY dots thus reduces the formation of the C dots andthe M dots. This gives a certain margin for the restriction of ink dutyand thereby delays the timing of starting the formation of K dots.

[0311] In the case of printing a gradation pattern from white to black,the use of the DY dots desirably delays the timings of startingformation of the C dots and the M dots and starting formation of the Kdots, thereby preventing the granularity from being worsened andimproving the picture quality of the resulting printed image.

[0312]FIG. 27C shows the results of the simulative computation withoutthe DY dots in the case of the printing paper having the restriction ofink duty equal to 260%. As clearly understood from the comparisonbetween the results of FIG. 27C and the results of FIG. 27A, the C dotsand the K dots start formation at substantially the same timings. In thecase of printing a gradation pattern from white to black, theimprovement in picture quality by the use of the DY dots is thussubstantially identical with the improvement in picture quality bychanging the restriction of ink duty set for the printing paper from220% to 260%.

[0313] The above results of the simulations suggest the usage of the DYink. In the case of printing a gradation pattern from white to black,the formation of dots with the DY ink starts prior to the formation ofdots with the C ink and the M ink. The DY ink has a hue closest to thatof the Y ink among the three basic color inks, C, M, and Y. Theformation of dots with the DY ink starts after the formation of dotswith the Y ink. The dots of the DY ink are more conspicuous than thedots of the Y ink. Formation of the dots of the DY ink in an overlappingmanner on the dots of the Y ink gives a printed image of high picturequality with less conspicuousness of dots. The dots of the DY ink may,however, be formed in place of the dots of the Y ink or simultaneouslywith the dots of the Y ink. The dots of the DY ink are not soconspicuous as-the dots of the C ink or the M ink. It is thus notnecessary to create the DY dots in an overlapping manner on the Y dots.Any of these arrangements does not cause the DY dots to be madeconspicuous and lower the picture quality of the resulting printedimage. The use of the DY ink desirably reduces the total quantity of inkconsumption.

[0314] There is another suggestion with regard to the usage of the DYink. In the case of printing a gradation pattern from white to black,formation of the dots with the DY ink starts after or simultaneouslywith the formation of dots with the LC ink and the LM ink. The DY inkhas a hue closest to that of the Y ink among the three basic color inks,C, M, and Y. It can thus be thought that the dots of the DY ink arecreated together with the dots of the LC ink and the dots of the LM ink.

[0315] The simulations discussed above aim at preventing thedeterioration of the granularity and improving the picture quality ofthe resulting printed image. When there is a margin for the restrictionof ink duty, the dots of the ink having less conspicuousness are thusselectively created. As long as there is no problem in granularity,however, the replacement of the LC dots with the C dots, the LM dotswith the M dots, and the Y dots with the DY dots may be commenced at theearlier timings than those discussed in the simulations. This makes thepoints of starting formation of the C dots, the M dots, the DY dots, andthe K dots closer to the value of 0% on the abscissa. According to thecondition 6 given above, it is possible to replace the same quantitiesof the Y dots, the LC dots, and the LM dots with the DY dots. Thereplacement with the DY dots at the earlier timing thus favorablyreduces the total quantity of ink consumption.

[0316] The use of the DY ink gives an image of better granularity underthe condition of a fixed quantity of total ink consumption or prints animage of equivalent picture quality with a less quantity of total inkconsumption. The appropriate setting can thus be selected for the use ofthe DY ink based on the priority to the picture quality, the priority tothe less quantity of total ink consumption, or the compatibility ofthese two effects.

[0317] As described above, the use of the DY ink improves thegranularity, which may be worsened by the conspicuousness of the cyandots, the magenta dots, or the black dots in a gradation pattern to theshadow area.

[0318] Dark cyan ink and dark magenta ink may also be used for the darkink. Like the dark yellow ink, these dark inks have the effects ofimproving the granularity based on the margin for the restriction of inkduty and saving the total quantity of ink consumption. The use of thedark cyan ink improves the granularity, which is worsened by the yellowdots and the magenta dots. Similarly the use of the dark magenta inkimproves the granularity, which is worsened by the yellow dots and thecyan dots. The yellow dots having a high lightness are, however,originally inconspicuous and are not the main factor of the worsenedgranularity. The use of the dark cyan ink thus improves the worsenedgranularity mainly due to the magenta dots. Similarly the use of thedark magenta ink improves the worsened granularity mainly due to thecyan dots. The use of the dark yellow ink, on the other hand, improvesthe worsened granularity due to both the cyan dots and the magenta dots,and is thus most effective. The dark yellow ink having the yellow dye asthe main component is less inconspicuous than the dark cyan ink or thedark magenta ink. From the viewpoint of the improved granularity, theuse of the dark yellow ink is most desirable.

[0319] C-4. Application to Printer with Four Color Inks

[0320] The above description regards the effects of the use of the DYink in the color printer using the six color inks C, M, Y, K, LC, andLM. The use of the DY ink, however, exerts the similar effects in thecolor printer using only the four color inks C, M, Y, and K and thecolor printer using only the three color inks C, M and Y.

[0321]FIGS. 28A, 28B, and 28C show results of simulations for confirmingthe effects of the use of the DY ink in the case of printing a gradationpattern from red to black with the color printer using only the fourcolor inks C, M, Y, and K. FIG. 28A shows the results of simulativecomputation of the dot recording ratio with regard to each color ink inthe case of printing with the DY dots on the printing paper having therestriction of ink duty equal to 220%. FIG. 28B shows the results ofsimulative computation of the dot recording ratio with regard to eachcolor ink in the case of printing without the DY dots on the printingpaper having the restriction of ink duty equal to 220%. FIG. 28C showsthe results of simulative computation of the dot recording ratio withregard to each color ink in the case of printing without the DY dots onthe printing paper having the restriction of ink duty equal to 260%.

[0322] The following effects are expected from the results of thesimulative computation shown in FIG. 28A. In the color printer usingonly the four color inks, since the LC ink is not used, it is requiredto start formation of the C dots at an early timing. As discussedpreviously, the C dots formed in the color of bright red are ratherconspicuous and significantly worsen the granularity. In the case withthe use of the DY ink as shown in FIG. 28A, the color of red isgradually darkened by replacing the Y dots with the DY dots. Theconspicuousness of the DY dots formed in the red background is as low asthat of the LC dots. The replacement of the Y dots with the DY dots thusdoes not worsen the granularity.

[0323] After the perfect replacement of all the Y dots with the DY dots,it is required to create the C dots. The formation of the DY dots hasalready lowered the lightness of the color ‘red’ to some extent (to thevalue of about 25% on the abscissa). Formation of the C dots thus doesnot significantly lower the granularity. The use of the DY ink delaysthe timing of starting formation of the C dots and thereby improves thegranularity.

[0324] In this simulative computation, since the DY ink contains thecomponents of the Y ink, the LC ink and the LM ink (see the condition 6given above), the formation of the DY dots decreases the dot recordingratio of the M dots. This gives a certain margin for the restriction ofink duty and delays the timing of starting formation of the K dots, thuspreventing the granularity from being worsened. As clearly understoodfrom the comparison between the results of the simulative computationwith the DY ink shown in FIG. 28A and the results of the simulativecomputation without the DY ink shown in FIG. 28B, the use of the DY inksignificantly delays the timing of starting formation of the K dots fromthe value of about 25% on the abscissa to the value of about 75%. Thismeans that the use of the DY ink remarkably prevents the granularityfrom being worsened.

[0325]FIG. 28C shows the results of the simulative computation withoutthe DY ink in the case of changing the restriction of ink duty set forthe printing paper from 220% to 260%. As clearly understood from thecomparison between FIG. 28B and FIG. 28C, the increase in restriction ofink duty delays the timing of starting formation of the K dots. Thecomparison between FIG. 28A and FIG. 28C, however, shows that theeffects attained by increasing the restriction of ink duty are less thanthe effects attained by the use of the DY ink. Even in the case of theprinting paper having the restriction of ink duty equal to 260%, the Cdots should start formation at the value of 0% on the abscissa. The useof the dark ink, on the other hand, delays the timing of startingformation of the C dots to the value of about 25% on the abscissa. Asdescribed previously, cyan is complementary to red. The C dots are thusrather conspicuous in the red background, although the degree ofconspicuousness is not so high as that of the K dots. The delayed timingof starting formation of the C dots to the value of about 25% on theabscissa by the use of the DY ink thus significantly improves thegranularity in the bright area (that is, the highlighted area).

[0326] As described above, in the process of printing a gradationpattern from red to black, the change to the printing paper having thehigher restriction of ink duty improves the picture quality only in theshadow area (that is, the area having large values on the abscissa). Theuse of the DY ink, on the other hand, improves the picture quality overthe whole range from the highlighted area to the shadow area.

[0327] C-5. Application to Printer with Three Color Inks

[0328]FIGS. 29A and 29B show the results of simulative computation inthe case of printing a gradation pattern from white to black with thecolor printer using only the C, M, and Y inks and not using the K ink.Unlike the ‘black’ color expressed by the K ink, the ‘black’ colorexpressed by a combination of the C, M, and Y inks does not have asufficiently low lightness and gives an impression of dimness. In thecase of printing the ‘black’ color with the C, M, and Y inks, all the Cdots, the M dots, and the Y dots should have dot recording ratios of100%. FIG. 29A shows the results of the simulative computation of thedot recording ratio with regard to each color ink in this state. The sumof the dot recording ratios of the respective color inks naturallyexceeds the restriction of ink duty, and such settings of the dotrecording ratios are not practical. In other words, only the dim blackcolor can be expressed by the color printer using the three color inks,as long as the practical dot recording ratios are set by taking intoaccount the restriction of ink duty.

[0329]FIG. 29B shows the results of the simulative computation of thedot recording ratio with regard to each ink in the case of using the DYdots in addition to the C, M, and Y dots. In this simulativecomputation, since the DY ink contains the components of the LC ink, theLM ink, and the Y ink (see the condition 6 given previously),replacement of the Y dots with the DY dots desirably decreases the dotrecording ratios of the C dots and the M dots. The use of the DY dotsaccordingly enables the expression of the color of sufficiently clearblack even when the practical dot recording ratios are set by takinginto account the restriction of ink duty.

[0330] As described above, the use of the DY ink enables the expressionof the color of sufficiently clear black even without the K ink. The useof the DY ink instead of the K ink ensures the expression of the colorof sufficiently clear black and enables the image of high picturequality to be printed with the color printer using the four color inksC, M, Y, and K and in the color printer using the six color inksincluding the LC and LM inks in addition to the above four color inks.In the prior art color printer using the four color inks or the sixcolor inks, attachment of the ink cartridge for the DY ink in place ofthe ink cartridge for the K ink with the required operations, forexample, rewriting the printer driver to a special printer driver forthe DY ink, enables formation of the DY dots and prints an image of highpicture quality including the sufficiently clear black color.

[0331] As described above with the results of the simulativecomputation, the use of the DY ink enhances the degree of freedom in dotformation and thus improves the picture quality under a variety ofprinting conditions. The enhanced degree of freedom with the use of theDY ink enables images of low lightness but high saturation to be printedadequately. In many cases, the desired color can not be expressed insuch images because of the restriction of ink duty. The use of the DYink relieves the restriction of ink duty and thereby enables the colorexpressed on the printing paper to be closer to the desired color.

[0332] In the simulative computation discussed above, the DY inksatisfying the above condition 6 was used as the DY ink. This DY ink issimilar to the DY1 ink shown in FIG. 14D. The use of another DY inksimilar to the DY2 ink also exerts the similar effects as discussedbelow.

[0333] Based on the theory of subtractive mixture of colors, it isassumed that the K ink is equivalent to the combination of identicalquantities of the C ink, the M ink, and the Y ink. According to theabove conditions 4 through 6, it is thought that the DY ink is obtainedby adding ¼ quantities of the C ink and the M ink to the Y ink. Sincethe K ink is equivalent to the combination of identical quantities ofthe C ink, the M ink, and the Y ink, the DY ink is thought to be themixture of ¾ quantity of the Y ink and ¼ quantity of the K ink. The inkthus obtained is similar to the DY2 ink shown in FIG. 14E. The effectsdescribed above with the DY ink under the above conditions are thus alsoexerted by the DY2 ink.

[0334] In the actual printing operation, the condition that the K ink isequivalent to the combination of identical quantities of the C ink, theM ink, and the Y ink is not strictly fulfilled. The DY2 ink is, however,expected to have the qualitatively similar effects to those of the DY1ink. The DY3 ink having the significantly different spectroscopiccharacteristics in the area of the low sensitivity of vision to thecolor may also be used as the DY ink.

[0335] The simulative computation discussed above is carried out underthe condition 6 that the DY ink is equivalent to the ink including theidentical quantities of the LC ink and the LM ink in addition to the Yink. The rates of the LC ink and the LM ink added to the Y ink are,however, not restricted to this condition. As shown in FIG. 12, thecontents of the cyan dye and the magenta dye included in the DY ink areapproximately one quarter the contents of the cyan dye and the magentadye included in the C ink and the M ink, respectively. The contents ofthe dyes included in the DY ink are, however, not restricted to thiscomposition. Possible modification may vary the contents of the cyan dyeand the magenta dye or change the ratio of the cyan dye to the magentadye.

[0336] The decrease in rates of the dyes included in the DY inkincreases the lightness of the DY ink. In this case, starting formationof the DY dots even in the state of a relatively high lightness (thatis, the state of a small value on the abscissa in the graphs of FIGS. 25through 29) does not make the DY dots conspicuous, thus not worseningthe granularity. The increase in rates of the dyes included in the DYink, on the other hand, enables reduction of the greater numbers of theother color dots by the formation of the DY dots. This accordinglyenhances the effects of improving the granularity based on the marginfor the restriction of ink duty and saving the total quantity of inkconsumption.

[0337] The present invention is not restricted to the above embodimentor its modifications, but there may be many other modifications,changes, and alterations without departing from the scope or spirit ofthe main characteristics of the present invention. For example, thesoftware or application programs that actualize the above functions maybe supplied through a communication line to the main memory of thecomputer system or an external storage device.

[0338] The scope and spirit of the present invention are limited only bythe terms of the appended claims.

What is claimed is:
 1. A printing system comprising a printer thatcreates dots with a plurality of different inks, so as to print an imageon a printing medium, and a print controller that supplies controlinformation to said printer, so as to control the creation of dots withthe plurality of different inks, wherein said print controllercomprises: a dot on-off condition specification unit that specifies doton-off conditions with regard to a plurality of basic color inks and adark ink based on input image data, the plurality of basic color inksbeing combined with one another to express achromatic color, the darkink having a main wavelength region of light absorption substantiallyidentical with that of one basic color ink selected out of the pluralityof basic color inks but a lower lightness than that of the selectedbasic color ink; and a control information output unit that outputs thecontrol information to specify the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to said printer, saidprinter comprising: a control information input unit that receives thecontrol information to specify the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink, which is output fromsaid control information output unit; and a dot formation unit thatcreates dots with the plurality of basic color inks and the dark ink,based on the input control information.
 2. A print controller thatsupplies control information to a printer, which creates dots with aplurality of different inks, in order to control the creation of dotswith the plurality of different inks, said printer creating dots with aplurality of basic color inks as well as with a dark ink, the pluralityof basic color inks being combined with, one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink, said print controllercomprising: a dot on-off condition specification unit that specifies doton-off conditions with regard to the plurality of basic color inks andthe dark ink, based on input image data; and a control informationoutput unit that outputs the control information to specify the doton-off conditions with regard to the plurality of basic color inks andthe dark ink to said printer.
 3. A print controller in accordance withclaim 2, wherein said dot on-off condition specification unit comprises:a memory which stores a color conversion table, in which each tint usedto express a color image is mapped to a combination of the plurality ofbasic color inks and the dark ink to represent the tint, said dot on-offcondition specification unit specifying the dot on-off conditions withregard to the plurality of basic color inks and the dark ink byreferring to said color conversion table.
 4. A print controller inaccordance with claim 2, wherein said dot on-off condition specificationunit specifies the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on a preset proportionregarding dots of the plurality of basic color inks and dots of the darkink.
 5. A print controller in accordance with claim 2, wherein the darkink has lower lightness and saturation than those of one basic color inkselected out of the plurality of basic color inks.
 6. A print controllerin accordance with claim 2, wherein the dark ink has a main wavelengthregion for most strongly absorbing a ray in a visible range, which issubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks, and a greater integral of lightabsorptivity in a wavelength region of the visible range than that ofthe selected basic color ink.
 7. A print controller in accordance withclaim 6, wherein the dark ink has the main wavelength region, which ismostly included in a wavelength region of 400 nm to 500 nm, and asmaller light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.
 8. A printcontroller in accordance with claim 6, wherein the dark ink has the mainwavelength region, which is mostly included in a wavelength region of400 nm to 500 nm, and a greater light absorptivity in the vicinity of700 nm than a mean light absorptivity in a wavelength region of 600 nmto 700 nm.
 9. A print controller in accordance with claim 2, wherein thedark ink has: (A) a characteristic wavelength region for stronglyabsorbing a ray in a visible range to mainly determine the hue of thedark ink, which is substantially identical with a characteristicwavelength region of one basic color ink selected out of the pluralityof basic color inks; (B) a mean value of light absorptivity that isgreater than or substantially identical with a mean value of lightabsorptivity of the selected basic color ink in the characteristicwavelength region of the dark ink; and (C) a mean value of lightabsorptivity that is greater than a mean value of light absorptivity ofthe selected basic color ink in a wavelength region of visible lightexcept the characteristic wavelength region of the dark ink.
 10. A printcontroller in accordance with claim 9, wherein the dark ink has thecharacteristic wavelength region, which is mostly included in awavelength region of 400 nm to 500 nm, and a smaller light absorptivityin the vicinity of 700 nm than a mean light absorptivity in a wavelengthregion of 600 nm to 700 nm.
 11. A print controller in accordance withclaim 9, wherein the dark ink has the characteristic wavelength region,which is mostly included in a wavelength region of 400 nm to 500 nm, anda greater light absorptivity in the vicinity of 700 nm than a mean lightabsorptivity in a wavelength region of 600 nm to 700 nm.
 12. A printcontroller in accordance with claim 2, wherein the dark ink has a hue ina specific hue range interposed between a red hue zone and a green huezone on a Munsell hue circle, and a lower lightness than that of a basiccolor ink out of the plurality of basic color inks, which has a hue inthe specific hue range.
 13. A print controller in accordance with claim12, wherein the dark ink has a hue in the specific hue range thatincludes a yellow hue zone and extends to a boundary between the yellowhue zone and the green hue zone on the Munsell hue circle.
 14. A printcontroller in accordance with claim .12, wherein the dark ink has a huein the specific hue range that includes a yellow hue zone and extends toa boundary between the yellow hue zone and the red hue zone on theMunsell hue circle, and a smaller saturation than that of flesh color.15. A print controller in accordance with claim 2, wherein the dark inkhas a hue included in a specific range of 10R to 10GY on a Munsell huecircle, and a lower lightness than that of a basic color ink out of theplurality of basic color inks, which has a hue in the specific range.16. A print controller in accordance with claim 15, wherein the dark inkhas a saturation of smaller than 3.5C on a Munsell chroma when the hueof the dark ink is in a range of 2.5YR to 7.5YR on the Munsell huecircle.
 17. A print controller in accordance with claim 15, wherein thehue of the dark ink is in a range of 10YR to 10GY on the Munsell huecircle.
 18. A print controller in accordance with claim 15, wherein thedark ink has the hue in a range of 10Y to 10R on the Munsell hue circleand a saturation of smaller than 3.5C on a Munsell chroma.
 19. A printcontroller in accordance with claim 2, wherein said printer creates dotswith the plurality of basic color inks and the dark ink, as well as dotswith at least one light ink, the at least one light ink having a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink, said dot on-off conditionspecification unit specifies the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink, as well as doton-off conditions with regard to the at least one light ink, and saidcontrol information output unit outputs the specification of the doton-off conditions with regard to the plurality of basic color inks, thedark ink, and the at least one light ink.
 20. A print controller inaccordance with claim 2, wherein said printer creates at least twovariable-size dots having different sizes with the plurality ofdifferent inks, said dot on-off condition specification unit specifiesthe dot on-off conditions with regard to the plurality of different inksand sizes of respective dots to be created by said printer, and saidcontrol information output unit outputs the specification of the doton-off conditions and the sizes of dots with regard to the plurality ofdifferent inks.
 21. A print controller in accordance with claim 2,wherein said printer creates dots with the plurality of basic color inksincluding at least yellow ink, as well as dots with dark yellow ink thathas a main wavelength region of light absorption substantially identicalwith that of the yellow ink but a lower lightness than that of theyellow ink, said dot on-off condition specification unit specifies doton-off conditions with regard to the plurality of basic color inks andthe dark yellow ink, and said control information output unit outputsthe specification of the dot on-off conditions with regard to theplurality of basic color inks and the dark yellow ink.
 22. A printcontroller in accordance with claim 2, wherein the plurality of basiccolor inks include at least cyan ink, magenta ink, and yellow ink, thedark ink having a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink, specification of thedot on-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created together with dots of atleast one of the basic color inks when an image to be printed has huesvarying from red to green on a Munsell hue circle.
 23. A printcontroller in accordance with claim 2, wherein the plurality of basiccolor inks include at least cyan ink, magenta ink, and yellow ink, thedark ink having a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink, specification of thedot on-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created prior to creation of dotswith either one of the cyan ink and the magenta ink when an image to beprinted has hues varying from yellow to black.
 24. A print controller inaccordance with claim 2, wherein the plurality of basic color inksinclude at least cyan ink, magenta ink, and yellow ink, the dark inkhaving a hue that is closest to the hue of the yellow ink among the cyanink, the magenta ink, and the yellow ink, and a lower lightness thanthat of the yellow ink, specification of the dot on-off conditions withregard to the dark ink being carried out to enable dots with the darkink to be created prior to creation of dots with either one of the cyanink and the magenta ink when an image to be printed has hues varyingfrom color of the either one of the cyan ink and the magenta ink toblack.
 25. A print controller in accordance with claim 2, wherein theplurality of basic color inks include at least cyan ink, magenta ink,and yellow ink, the dark ink having a hue that is closest to the hue ofthe yellow ink among the cyan ink, the magenta ink, and the yellow ink,and a lower lightness than that of the yellow ink, specification of thedot on-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created after creation of dots withthe yellow ink when an image to be printed has hues varying from colorof either one of the cyan ink and the magenta ink to black.
 26. A printcontroller in accordance with claim 19, wherein the plurality of basiccolor inks include at least cyan ink, magenta ink, and yellow ink, thedark ink having a hue that is closest to the hue of the yellow ink amongthe cyan ink, the magenta ink, and the yellow ink, specification of thedot on-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created after creation of dots withthe light ink when an image to be printed has hues varying from yellowto black.
 27. A print controller in accordance with claim 26, whereinthe light ink is light cyan ink having a hue substantially identicalwith that of the cyan ink but a lower density than that of the cyan ink.28. A print controller in accordance with claim 26, wherein the lightink is light magenta ink having a hue substantially identical with thatof the magenta ink but a lower density than that of the magenta ink. 29.A print controller in accordance with claim 26, wherein the dark inkhaving a hue that is closest to the hue of the yellow ink among the cyanink, the magenta ink, and the yellow ink, specification of the doton-off conditions with regard to the dark ink being carried out toenable dots with the dark ink to be created after creation of both dotswith light cyan ink, which has a hue substantially identical with thatof the cyan ink but a lower density than that of the cyan ink, and dotswith light magenta ink, which has a hue substantially identical withthat of the magenta ink but a lower density than that of the magentaink, when an image to be printed has hues varying from yellow to black.30. A print controller that supplies control information to a printer,which creates dots with a plurality of different inks, in order tocontrol the creation of dots with the plurality of different inks, saidprinter creating dots with a plurality of basic color inks, whichinclude at least cyan ink, magenta ink, and yellow ink, as well as withdark yellow ink, the dark yellow ink having a main wavelength region oflight absorption substantially identical with that of the yellow ink buta lower lightness than that of the yellow ink, said print controllercomprising: a dot on-off condition specification unit that specifies doton-off conditions with regard to the plurality of basic color inks andthe dark yellow ink, based on input image data; and a controlinformation output unit that outputs the specification of the dot on-offconditions with regard to the plurality of basic color inks and the darkyellow ink to said printer as the control information.
 31. A printingapparatus that has a print head to create dots with a plurality ofdifferent inks on a printing medium, receives control information tocontrol the creation of dots with the plurality of different inks, andactually creates dots with the plurality of different inks, based on theinput control information, so as to print an image, said printingapparatus comprising: a basic color ink supply unit that supplies aplurality of basic color inks to said print head, the plurality of basiccolor inks being combined with one another to express achromatic color;a dark ink supply unit that supplies a dark ink to said print head, thedark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; a control information input unit that receivesthe control information with regard to dots of the plurality of basiccolor inks and the dark ink; and a dot formation unit that drives saidprint head based on the input control information, so as to create dotswith the plurality of basic color inks and the dark ink.
 32. A printingapparatus in accordance with claim 31, wherein the plurality of basiccolor inks include at least cyan ink, magenta ink, and yellow ink.
 33. Aprinting apparatus in accordance with claim 31, wherein the plurality ofbasic color inks include at least cyan ink, magenta ink, yellow ink, andblack ink and the dark ink is dark yellow ink having a main wavelengthregion of light absorption substantially identical with that of theyellow ink but a lower lightness than that of the yellow ink.
 34. Aprinting apparatus in accordance with claim 31, said printing apparatuscomprising: a light ink supply unit that supplies at least one light inkto said print head, the at least one light ink having a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink, wherein said controlinformation input unit receives the control information with regard todots of the at least one light ink, as well as with regard to the dotsof the plurality of basic color inks and the dark ink, and said dotformation unit creates dots with the at least one light ink as well asthe plurality of basic color inks and the dark ink, based on the inputcontrol information.
 35. A printing apparatus in accordance with claim31, wherein said print head enables at least two variable-size dotshaving different sizes to be created, said control information inputunit receives pieces of information regarding dot on-off conditions andsizes of dots to be formed by said print head with regard to theplurality of different inks as the control information, and said dotformation unit creates the at least two variable-size dots with theplurality of different inks, based on the input control information. 36.A printing apparatus in accordance with claim 31, said printingapparatus having an ink reservoir unit, in which the plurality of basiccolor inks and the dark ink are kept independently.
 37. A printingapparatus in accordance with claim 36, wherein said ink reservoir unitkeeps a greater quantity of the dark ink than a quantity of the onebasic color ink corresponding to the dark ink.
 38. A printing apparatusthat has a print head to create dots with a plurality of different inkson a printing medium, receives control information to control thecreation of dots with the plurality of different inks, and actuallycreates dots with the plurality of different inks, based on the inputcontrol information, so as to print an image, said printing apparatuscomprising: a basic color ink supply unit that supplies a plurality ofbasic color inks to said print head, the plurality of basic color inksincluding at least cyan ink, magenta ink, and yellow ink; a dark yellowink supply unit that supplies dark yellow ink to said print head, thedark yellow ink having a main wavelength region of light absorptionsubstantially identical with that of the yellow ink inks but a lowerlightness than that of the yellow ink; a control information input unitthat receives the control information with regard to dots of theplurality of basic color inks and the dark yellow ink; and a dotformation unit that drives said print head based on the input controlinformation, so as to create dots with the plurality of basic color inksand the dark yellow ink.
 39. A printing apparatus in accordance withclaim 38, said printing apparatus having an ink reservoir unit, in whichat least the cyan ink, the magenta ink, the yellow ink, and the darkyellow ink are kept independently, said ink reservoir unit keeping agreater quantity of the dark yellow ink than a quantity of the yellowink.
 40. A method of creating dots with a plurality of different inks,so as to print an image on a printing medium, said method comprising thesteps of: specifying dot on-off conditions with regard to a plurality ofbasic color inks and a dark ink based on input image data, the pluralityof basic color inks being combined with one another to expressachromatic color, the dark ink having a main wavelength region of lightabsorption substantially identical with that of one basic color inkselected out of the plurality of basic color inks but a lower lightnessthan that of the selected basic color ink; and creating dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink, so as to print an image.
 41. Amethod of supplying control information to a printer, which creates dotswith a plurality of different inks on a printing medium, in order tocontrol the creation of dots with the plurality of different inks andthereby controlling a printing operation of said printer, said methodcomprising the steps of: (a) specifying dot on-off conditions withregard to a plurality of basic color inks and a dark ink based on inputimage data, the plurality of basic color inks being combined with oneanother to express achromatic color, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink; and (b)outputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark ink to said printer asthe control information, so as to control the printing operation of saidprinter.
 42. A method in accordance with claim 41, said method furthercomprising the step of: (c) storing in advance mappings of tints used toexpress a color image to combinations of the plurality of basic colorinks and the dark ink to represent the tints, wherein said step (b)specifies the dot on-off conditions with regard to the plurality ofbasic color inks and the dark ink, based on the mappings stored inadvance.
 43. A method of supplying control information to a printer,which creates dots with a plurality of different inks on a printingmedium,. in order to control the creation of dots with the plurality ofdifferent inks and thereby controlling a printing operation of saidprinter, said method comprising the steps of: (a) specifying dot on-offconditions with regard to a plurality of basic color inks and darkyellow ink based on input image data, the plurality of basic color inksincluding at least cyan ink, magenta ink, and yellow ink, the darkyellow ink having a main wavelength region of light absorptionsubstantially identical with that of the yellow ink but a lowerlightness than that of the yellow ink; and (b) outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark yellow ink to said printer as thecontrol information, so as to control the printing operation of saidprinter.
 44. A method of receiving control information to controlcreation of dots with a plurality of different inks and driving a printhead, which creates dots with the plurality of different inks on aprinting medium, based on the control information, so as to print animage, said method comprising the steps of: (a) supplying a plurality ofbasic color inks and a dark ink to said print head, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; (b) receiving the control information withregard to dots of the plurality of basic color inks and the dark ink;and (c) driving said print head based on the input control informationto create dots with the plurality of basic color inks and the dark ink,thereby printing an image.
 45. A method of receiving control informationto control creation of dots with a plurality of different inks anddriving a print head, which creates dots with the plurality of differentinks on a printing medium, based on the control information, so as toprint an image, said method comprising the steps of: (a) supplying aplurality of basic color inks and dark yellow ink to said print head,the plurality of basic color inks including at least cyan ink, magentaink, and yellow ink, the dark yellow ink having a main wavelength regionof light absorption substantially identical with that of the yellow inkbut a lower lightness than that of the yellow ink; (b) receiving thecontrol information with regard to dots of the plurality of basic colorinks and the dark yellow ink; and (c) driving said print head based onthe input control information to create dots with the plurality of basiccolor inks and the dark yellow ink, thereby printing an image.
 46. Anink cartridge detachably attached to a printing apparatus, which printsan image with a plurality of basic color inks, the plurality of basiccolor inks being combined with one another to express achromatic color,said ink cartridge keeping therein at least one ink to be supplied tosaid printing apparatus, said ink cartridge comprising: a dark inkreservoir that keeps therein a dark ink, the dark ink having a mainwavelength region of light absorption substantially identical with thatof one basic color ink selected out of the plurality of basic color inksbut a lower lightness than that of the selected basic color ink.
 47. Anink cartridge in accordance with claim 46, wherein the dark ink haslower lightness and saturation than those of one basic color inkselected out of the plurality of basic color inks.
 48. An ink cartridgein accordance with claim 46, wherein the dark ink has a main wavelengthregion for most strongly absorbing a ray in a visible range, which issubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks, and a greater integral of lightabsorptivity in a wavelength region of the visible range than that ofthe selected basic color ink.
 49. An ink cartridge in accordance withclaim 46, wherein the dark ink has: (A) a characteristic wavelengthregion for strongly absorbing a ray in a visible range to mainlydetermine the hue of the dark ink, which is substantially identical witha characteristic wavelength region of one basic color ink selected outof the plurality of basic color inks; (B) a mean value of lightabsorptivity that is greater than or substantially identical with a meanvalue of light absorptivity of the selected basic color ink in thecharacteristic wavelength region of the dark ink; and (C) a mean valueof light absorptivity that is greater than a mean value of lightabsorptivity of the selected basic color ink in a wavelength region ofvisible light except the characteristic wavelength region of the darkink.
 50. An ink cartridge in accordance with claim 46, said inkcartridge further comprising: a basic color ink reservoir that keepstherein one basic color ink selected out of the plurality of basic colorinks.
 51. An ink cartridge in accordance with claim 46, said inkcartridge further comprising: a black ink reservoir that keeps thereinblack ink, which is achromatic and has a low lightness.
 52. An inkcartridge in accordance with claim 46, said ink cartridge furthercomprising: a light ink reservoir that keeps therein at least one lightink, which has a hue substantially identical with that of at least onebasic color ink selected out of the plurality of basic color inks but alower density than that of the at least one basic color ink.
 53. An inkcartridge in accordance with claim 46, said ink cartridge furthercomprising: a basic color ink reservoir that keeps therein one basiccolor ink selected out of the plurality of basic color inks; and a lightink reservoir that keeps therein at least one light ink, which has a huesubstantially identical with that of at least one basic color inkselected out of the plurality of basic color inks but a lower densitythan that of the at least one basic color ink.
 54. An ink cartridgedetachably attached to a printing apparatus, which prints an image withat least one ink, said ink cartridge keeping therein at least one ink tobe supplied to said printing apparatus, said ink cartridge comprising: adark yellow ink reservoir that keeps therein dark yellow ink, the darkyellow ink having: (A) a characteristic wavelength region that is mostlyin a wavelength range of 400 nm to 500 nm, the characteristic wavelengthregion strongly absorbing a ray in a visible range to mainly determinethe hue of the dark yellow ink; and (B) a mean value of absorptivity ofthe ray in the visible range except the characteristic wavelengthregion, which ranges from 10% to 60%.
 55. An ink cartridge detachablyattached to a printing apparatus, which prints an image with at leastone ink, said ink cartridge keeping therein at least one ink to besupplied to said printing apparatus, said ink cartridge comprising: adark yellow ink reservoir that keeps therein dark yellow ink, the darkyellow ink having: (A) a hue included in a specific range of 10R to 10GYon a Munsell hue circle; and (B) a saturation of smaller than 3.5C on aMunsell chroma.
 56. An ink cartridge detachably attached to a printingapparatus, which prints an image with at least one ink, said inkcartridge keeping therein at least one ink to be supplied to saidprinting apparatus, said ink cartridge comprising: an yellow inkreservoir that keeps yellow ink therein; and a dark yellow ink reservoirthat keeps therein dark yellow ink, which has a lower lightness thanthat of the yellow ink.
 57. An ink reservoir in accordance with claim56, wherein the dark yellow ink reservoir has a greater capacity thanthat of the yellow ink reservoir.
 58. An ink cartridge detachablyattached to a printing apparatus, which prints an image with at leastone ink, said ink cartridge keeping therein at least one ink to besupplied to said printing apparatus, said ink cartridge comprising: ablack ink reservoir that keeps therein black ink, which is achromaticand has a low lightness; and a dark yellow ink reservoir that keepstherein dark yellow ink, which has a lower lightness than that of yellowink.
 59. An ink cartridge detachably attached to a printing apparatus,which prints an image with at least one ink, said ink cartridge keepingtherein at least one ink to be supplied to said printing apparatus, saidink cartridge comprising: a dark yellow ink reservoir that keeps thereindark yellow ink, which has a lower lightness than that of yellow ink; alight cyan ink reservoir that keeps therein light cyan ink, which has alower density than that of cyan ink; and a light magenta ink reservoirthat keeps therein light magenta ink, which has a lower density thanthat of magenta ink.
 60. An ink cartridge detachably attached to aprinting apparatus, which prints an image with at least one ink, saidink cartridge keeping therein at least one ink to be supplied to saidprinting apparatus, said ink cartridge comprising: an yellow inkreservoir that keeps yellow ink therein; a dark yellow ink reservoirthat keeps therein dark yellow ink, which has a lower lightness thanthat of the yellow ink; a cyan ink reservoir that keeps cyan inktherein; a light cyan ink reservoir that keeps therein light cyan ink,which has a lower density than that of the cyan ink; a magenta inkreservoir that keeps magenta ink therein; and a light magenta inkreservoir that keeps therein light magenta ink, which has a lowerdensity than that of the magenta ink.
 61. An ink cartridge in accordancewith claim 60, wherein the dark yellow ink reservoir has a greatercapacity than that of the yellow ink reservoir.
 62. An ink cartridge inaccordance with any one of claim 46 and claims 54 through 61, said inkcartridge further comprising: a storage device that stores informationregarding a quantity of ink in each of the ink reservoirs in a readable,writable, and volatile manner.
 63. An ink cartridge in accordance withclaim 62, wherein said storage device has an ink quantity informationstorage area, which is accessed to be written first by said printingapparatus and in which the information regarding the quantity of ink ineach of the ink reservoirs is stored.
 64. An ink supplier that feeds asupply of ink to an ink cartridge, said ink cartridge being detachablyattached to a printing apparatus and keeping therein at least one inkused by said printing apparatus, said ink supplier comprising: a sealedink reservoir that keeps an ink in a sealing manner; and an ink supplyunit that feeds a supply of the sealed ink to said ink cartridge,wherein the ink sealed in said sealed ink reservoir has: (A) acharacteristic wavelength region that is mostly included in a wavelengthrange of 400 nm to 500 nm, the characteristic wavelength region stronglyabsorbing a ray in a visible range to mainly determine the hue of theink; and (B) a mean value of absorptivity of the ray in the visiblerange except the characteristic wavelength region, which ranges from 10%to 60%.
 65. An ink supplier that feeds a supply of ink to an inkcartridge, said ink cartridge being detachably attached to a printingapparatus and keeping therein at least one ink used by said printingapparatus, said ink supplier comprising: a sealed ink reservoir thatkeeps an ink in a sealing manner; and an ink supply unit that feeds asupply of the sealed ink to said ink cartridge, wherein the ink sealedin said sealed ink reservoir has: (A) a hue included in a specific rangeof 10R to 10GY on a Munsell hue circle; and (B) a saturation of smallerthan 3.5C on a Munsell chroma.
 66. A recording medium, in which aspecific program is recorded in a computer readable manner, saidspecific program actualizing a method of creating dots with a pluralityof different inks, so as to print an image on a printing medium, saidspecific program causing a computer to attain the functions of:specifying dot on-off conditions with regard to a plurality of basiccolor inks and a dark ink based on input image data, the plurality ofbasic color inks being combined with one another to express achromaticcolor, the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and controlling creation of dots with theplurality of basic color inks and the dark ink, based on thespecification of the dot-on-off conditions with regard to the pluralityof basic color inks and the dark ink.
 67. A recording medium, in which aspecific program is recorded in a computer readable manner, saidspecific program actualizing a method of supplying control informationto a printer, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof said printer, said specific program causing a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and a dark ink based on input image data,the plurality of basic color inks being combined with one another toexpress achromatic color, the dark ink having a main wavelength regionof light absorption substantially identical with that of one basic colorink selected out of the plurality of basic color inks but a lowerlightness than that of the selected basic color ink; and outputting thespecification of the dot on-off conditions with regard to the pluralityof basic color inks and the dark ink to said printer as the controlinformation, so as to control the printing operation of said printer.68. A recording medium in accordance with claim 67, wherein saidspecific program further causes the computer to attain the function of:storing in advance mappings of tints used to express a color image tocombinations of the plurality of basic color inks and the dark ink torepresent the tints, and the dot on-off conditions with regard to theplurality of basic color inks and the dark ink are specified, based onthe mappings stored in advance.
 69. A recording medium, in which aspecific program is recorded in a computer readable manner, saidspecific program actualizing a method of supplying control informationto a printer, which creates dots with a plurality of different inks on aprinting medium, in order to control the creation of dots with theplurality of different inks and thereby controlling a printing operationof said printer, said specific program causing a computer to attain thefunctions of: specifying dot on-off conditions with regard to aplurality of basic color inks and dark yellow ink based on input imagedata, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; andoutputting the specification of the dot on-off conditions with regard tothe plurality of basic color inks and the dark yellow ink to saidprinter as the control information, so as to control the printingoperation of said printer.
 70. A recording medium, in which a specificprogram is recorded in a computer readable manner, said specific programactualizing a method of receiving control information to controlcreation of dots with a plurality of different inks and driving a printhead, which creates dots with the plurality of different inks on aprinting medium, based on the control information, so as to print animage, said specific program causing a computer to attain the functionsof: receiving the control information to control creation of dots with aplurality of basic color inks and a dark ink, the plurality of basiccolor inks being combined with one another to express achromatic color,the dark ink having a main wavelength region of light absorptionsubstantially identical with that of one basic color ink selected out ofthe plurality of basic color inks but a lower lightness than that of theselected basic color ink; and driving said print head based on the inputcontrol information to create dots with the plurality of basic colorinks and the dark ink, thereby printing an image.
 71. A recordingmedium, in which a specific program is recorded in a computer readablemanner, said specific program actualizing a method of receiving controlinformation to control creation of dots with a plurality of differentinks and driving a print head, which creates dots with the plurality ofdifferent inks on a printing medium, based on the control information,so as to print an image, said specific program causing a computer toattain the functions of: receiving the control information to controlcreation of dots with a plurality of basic color inks and dark yellowink, the plurality of basic color inks including at least cyan ink,magenta ink, and yellow ink, the dark yellow ink having a mainwavelength region of light absorption substantially identical with thatof the yellow ink but a lower lightness than that of the yellow ink; anddriving said print head based on the input control information to createdots with the plurality of basic color inks and the dark yellow ink,thereby printing an image.